Copy std::map into std::vector of pairs
17
I'm trying to copy a map into a vector of pair, so I can then sort the vector by the second data member of the pairs. I have resolved this doing like this:
void mappedWordsListSorter(){
for (auto itr = mappedWordsList.begin(); itr != mappedWordsList.end(); ++itr){
vectorWordsList.push_back(*itr);
}
sort(vectorWordsList.begin(), vectorWordsList.end(), [=](pair<string, int>& a, pair<string, int>& b){return a.second > b.second;});
}
I need to find a way to do this without using a raw loop, using the standard library instead. I have come across a lot of examples doing this by only transferring either the keys or the values of the map. I need to copy into a vector of pairs<string, int>. What is the best way to do it?
c++ stdvector stdmap c++-standard-library std-pair
edited Dec 19 '18 at 20:49
Deduplicator
34.4k64888
asked Dec 19 '18 at 15:33
VictorVictor
862
|
show 4 more comments
17
I'm trying to copy a map into a vector of pair, so I can then sort the vector by the second data member of the pairs. I have resolved this doing like this:
void mappedWordsListSorter(){
for (auto itr = mappedWordsList.begin(); itr != mappedWordsList.end(); ++itr){
vectorWordsList.push_back(*itr);
}
sort(vectorWordsList.begin(), vectorWordsList.end(), [=](pair<string, int>& a, pair<string, int>& b){return a.second > b.second;});
}
I need to find a way to do this without using a raw loop, using the standard library instead. I have come across a lot of examples doing this by only transferring either the keys or the values of the map. I need to copy into a vector of pairs<string, int>. What is the best way to do it?
c++ stdvector stdmap c++-standard-library std-pair
edited Dec 19 '18 at 20:49
Deduplicator
34.4k64888
asked Dec 19 '18 at 15:33
VictorVictor
862
1
@Lorand - The sort happens on theseconditem in the pair, which is not the key.
– StoryTeller
Dec 19 '18 at 15:37
1
@Lorand It seems that OP wants to perform the sort based on the values, not the keys.
– ネロク
Dec 19 '18 at 15:38
3
Seems like that question should be flagged as a duplicate of this one, since the answer provided by @NathanOliver is way better than any of the answers to that question. Edit : Though that question includes sorting the result.
– François Andrieux
Dec 19 '18 at 15:40
1
@ALX23z - I agree that[=]should not be present. But just because it's there doesn't mean everything gets copied. The lambda has to use something from the surrounding scope to capture it.
– StoryTeller
Dec 19 '18 at 15:46
1
@ALX23z Actually, it will only copy a variable is you use it in the lambda body. There is no performance penalty to use[=]if you don't use any of the variables in scope.
– NathanOliver
Dec 19 '18 at 15:46
|
show 4 more comments
17
17
17
1
I'm trying to copy a map into a vector of pair, so I can then sort the vector by the second data member of the pairs. I have resolved this doing like this:
void mappedWordsListSorter(){
for (auto itr = mappedWordsList.begin(); itr != mappedWordsList.end(); ++itr){
vectorWordsList.push_back(*itr);
}
sort(vectorWordsList.begin(), vectorWordsList.end(), [=](pair<string, int>& a, pair<string, int>& b){return a.second > b.second;});
}
I need to find a way to do this without using a raw loop, using the standard library instead. I have come across a lot of examples doing this by only transferring either the keys or the values of the map. I need to copy into a vector of pairs<string, int>. What is the best way to do it?
c++ stdvector stdmap c++-standard-library std-pair
edited Dec 19 '18 at 20:49
Deduplicator
34.4k64888
asked Dec 19 '18 at 15:33
VictorVictor
862
I'm trying to copy a map into a vector of pair, so I can then sort the vector by the second data member of the pairs. I have resolved this doing like this:
void mappedWordsListSorter(){
for (auto itr = mappedWordsList.begin(); itr != mappedWordsList.end(); ++itr){
vectorWordsList.push_back(*itr);
}
sort(vectorWordsList.begin(), vectorWordsList.end(), [=](pair<string, int>& a, pair<string, int>& b){return a.second > b.second;});
}
I need to find a way to do this without using a raw loop, using the standard library instead. I have come across a lot of examples doing this by only transferring either the keys or the values of the map. I need to copy into a vector of pairs<string, int>. What is the best way to do it?
c++ stdvector stdmap c++-standard-library std-pair
c++ stdvector stdmap c++-standard-library std-pair
edited Dec 19 '18 at 20:49
Deduplicator
34.4k64888
asked Dec 19 '18 at 15:33
VictorVictor
862
edited Dec 19 '18 at 20:49
Deduplicator
34.4k64888
asked Dec 19 '18 at 15:33
VictorVictor
862
edited Dec 19 '18 at 20:49
Deduplicator
34.4k64888
edited Dec 19 '18 at 20:49
Deduplicator
34.4k64888
edited Dec 19 '18 at 20:49
Deduplicator
34.4k64888
34.4k64888
asked Dec 19 '18 at 15:33
VictorVictor
862
asked Dec 19 '18 at 15:33
VictorVictor
862
asked Dec 19 '18 at 15:33
VictorVictor
862
862
1
@Lorand - The sort happens on theseconditem in the pair, which is not the key.
– StoryTeller
Dec 19 '18 at 15:37
1
@Lorand It seems that OP wants to perform the sort based on the values, not the keys.
– ネロク
Dec 19 '18 at 15:38
3
Seems like that question should be flagged as a duplicate of this one, since the answer provided by @NathanOliver is way better than any of the answers to that question. Edit : Though that question includes sorting the result.
– François Andrieux
Dec 19 '18 at 15:40
1
@ALX23z - I agree that[=]should not be present. But just because it's there doesn't mean everything gets copied. The lambda has to use something from the surrounding scope to capture it.
– StoryTeller
Dec 19 '18 at 15:46
1
@ALX23z Actually, it will only copy a variable is you use it in the lambda body. There is no performance penalty to use[=]if you don't use any of the variables in scope.
– NathanOliver
Dec 19 '18 at 15:46
|
show 4 more comments
1
@Lorand - The sort happens on theseconditem in the pair, which is not the key.
– StoryTeller
Dec 19 '18 at 15:37
1
@Lorand It seems that OP wants to perform the sort based on the values, not the keys.
– ネロク
Dec 19 '18 at 15:38
3
Seems like that question should be flagged as a duplicate of this one, since the answer provided by @NathanOliver is way better than any of the answers to that question. Edit : Though that question includes sorting the result.
– François Andrieux
Dec 19 '18 at 15:40
1
@ALX23z - I agree that[=]should not be present. But just because it's there doesn't mean everything gets copied. The lambda has to use something from the surrounding scope to capture it.
– StoryTeller
Dec 19 '18 at 15:46
1
@ALX23z Actually, it will only copy a variable is you use it in the lambda body. There is no performance penalty to use[=]if you don't use any of the variables in scope.
– NathanOliver
Dec 19 '18 at 15:46
1
1
@Lorand - The sort happens on the
second item in the pair, which is not the key.– StoryTeller
Dec 19 '18 at 15:37
@Lorand - The sort happens on the
second item in the pair, which is not the key.– StoryTeller
Dec 19 '18 at 15:37
1
1
@Lorand It seems that OP wants to perform the sort based on the values, not the keys.
– ネロク
Dec 19 '18 at 15:38
@Lorand It seems that OP wants to perform the sort based on the values, not the keys.
– ネロク
Dec 19 '18 at 15:38
3
3
Seems like that question should be flagged as a duplicate of this one, since the answer provided by @NathanOliver is way better than any of the answers to that question. Edit : Though that question includes sorting the result.
– François Andrieux
Dec 19 '18 at 15:40
Seems like that question should be flagged as a duplicate of this one, since the answer provided by @NathanOliver is way better than any of the answers to that question. Edit : Though that question includes sorting the result.
– François Andrieux
Dec 19 '18 at 15:40
1
1
@ALX23z - I agree that
[=] should not be present. But just because it's there doesn't mean everything gets copied. The lambda has to use something from the surrounding scope to capture it.– StoryTeller
Dec 19 '18 at 15:46
@ALX23z - I agree that
[=] should not be present. But just because it's there doesn't mean everything gets copied. The lambda has to use something from the surrounding scope to capture it.– StoryTeller
Dec 19 '18 at 15:46
1
1
@ALX23z Actually, it will only copy a variable is you use it in the lambda body. There is no performance penalty to use
[=] if you don't use any of the variables in scope.– NathanOliver
Dec 19 '18 at 15:46
@ALX23z Actually, it will only copy a variable is you use it in the lambda body. There is no performance penalty to use
[=] if you don't use any of the variables in scope.– NathanOliver
Dec 19 '18 at 15:46
|
show 4 more comments
3 Answers
3
active
oldest
votes
22
Just use std::vector's assign member function.
//no need to call reserve, bidirectional iterators or better will compute the size and reserve internally.
vectorWordsList.assign(mappedWordsList.begin(), mappedWordsList.end());
If you have existing values in the vector that you don't want overwritten then use insert instead like
vectorWordsList.reserve(vectorWordsList.size() + mappedWordsList.size()); // make sure we only have a single memory allocation
vectorWordsList.insert(vectorWordsList.end(), mappedWordsList.begin(), mappedWordsList.end());
answered Dec 19 '18 at 15:38
NathanOliverNathanOliver
90.2k15126190
1
I would hope thatassignwould essentiallyreserveinternally.
– François Andrieux
Dec 19 '18 at 15:41
10
@FrançoisAndrieux It most likely would if you passed random access iterators but sincemaphas bidirectional iterators it requires a traversal to known how many elements to allocate space for so it isn't going to do that.
– NathanOliver
Dec 19 '18 at 15:43
1
@NathanOliver libstdc++ actually does essentiallyreserveinternally. For any ForwardIterator, it will callstd::distance, paying for a traversal for anything less than a RandomAccessIterator. You can tracestd::vector::assignto here.
– Justin
Dec 19 '18 at 19:43
1
@Justin Cool. Thanks for finding that. I still like to be explicit, in case other implementations don't do this.
– NathanOliver
Dec 19 '18 at 19:47
Putting a.resize(0)before.reserve()might be an optimization if the elements should be replaced.
– Deduplicator
Dec 19 '18 at 20:46
|
show 2 more comments
7
You can use std::copy and std::back_inserter:
std::copy(mappedWordsList.begin(),
mappedWordsList.end(),
std::back_inserter(vectorWordsList));
Honestly, I think that a range-for loop is clearer:
for(const auto& kv : mappedWordsList)
vectorWordsList.emplace_back(kv);
Regardless, you can use std::vector::reserve to preallocate memory on your target vector, avoiding unnecessary reallocations.
answered Dec 19 '18 at 15:35
Vittorio RomeoVittorio Romeo
57.8k17156299
add a comment |
7
It's worth noting that if you are creating a vector for this purpose, you may use the vector's constructor directly:
std::vector<std::pair<FirstType,SecondType>> vectorWordsList( mappedWordsList.begin(), mappedWordsList.end() );
In C++17, you may also omit the vector's template arguments to have the compiler deduce them:
std::vector vectorWordsList( mappedWordsList.begin(), mappedWordsList.end() );
answered Dec 19 '18 at 21:18
Drew DormannDrew Dormann
41.6k979142
Unless you want to create a vector of iterators, you need parens.
– T.C.
Dec 20 '18 at 12:00
@T.C. thank you!
– Drew Dormann
Dec 20 '18 at 16:18
add a comment |
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3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
22
Just use std::vector's assign member function.
//no need to call reserve, bidirectional iterators or better will compute the size and reserve internally.
vectorWordsList.assign(mappedWordsList.begin(), mappedWordsList.end());
If you have existing values in the vector that you don't want overwritten then use insert instead like
vectorWordsList.reserve(vectorWordsList.size() + mappedWordsList.size()); // make sure we only have a single memory allocation
vectorWordsList.insert(vectorWordsList.end(), mappedWordsList.begin(), mappedWordsList.end());
answered Dec 19 '18 at 15:38
NathanOliverNathanOliver
90.2k15126190
1
I would hope thatassignwould essentiallyreserveinternally.
– François Andrieux
Dec 19 '18 at 15:41
10
@FrançoisAndrieux It most likely would if you passed random access iterators but sincemaphas bidirectional iterators it requires a traversal to known how many elements to allocate space for so it isn't going to do that.
– NathanOliver
Dec 19 '18 at 15:43
1
@NathanOliver libstdc++ actually does essentiallyreserveinternally. For any ForwardIterator, it will callstd::distance, paying for a traversal for anything less than a RandomAccessIterator. You can tracestd::vector::assignto here.
– Justin
Dec 19 '18 at 19:43
1
@Justin Cool. Thanks for finding that. I still like to be explicit, in case other implementations don't do this.
– NathanOliver
Dec 19 '18 at 19:47
Putting a.resize(0)before.reserve()might be an optimization if the elements should be replaced.
– Deduplicator
Dec 19 '18 at 20:46
|
show 2 more comments
22
Just use std::vector's assign member function.
//no need to call reserve, bidirectional iterators or better will compute the size and reserve internally.
vectorWordsList.assign(mappedWordsList.begin(), mappedWordsList.end());
If you have existing values in the vector that you don't want overwritten then use insert instead like
vectorWordsList.reserve(vectorWordsList.size() + mappedWordsList.size()); // make sure we only have a single memory allocation
vectorWordsList.insert(vectorWordsList.end(), mappedWordsList.begin(), mappedWordsList.end());
answered Dec 19 '18 at 15:38
NathanOliverNathanOliver
90.2k15126190
1
I would hope thatassignwould essentiallyreserveinternally.
– François Andrieux
Dec 19 '18 at 15:41
10
@FrançoisAndrieux It most likely would if you passed random access iterators but sincemaphas bidirectional iterators it requires a traversal to known how many elements to allocate space for so it isn't going to do that.
– NathanOliver
Dec 19 '18 at 15:43
1
@NathanOliver libstdc++ actually does essentiallyreserveinternally. For any ForwardIterator, it will callstd::distance, paying for a traversal for anything less than a RandomAccessIterator. You can tracestd::vector::assignto here.
– Justin
Dec 19 '18 at 19:43
1
@Justin Cool. Thanks for finding that. I still like to be explicit, in case other implementations don't do this.
– NathanOliver
Dec 19 '18 at 19:47
Putting a.resize(0)before.reserve()might be an optimization if the elements should be replaced.
– Deduplicator
Dec 19 '18 at 20:46
|
show 2 more comments
22
22
22
Just use std::vector's assign member function.
//no need to call reserve, bidirectional iterators or better will compute the size and reserve internally.
vectorWordsList.assign(mappedWordsList.begin(), mappedWordsList.end());
If you have existing values in the vector that you don't want overwritten then use insert instead like
vectorWordsList.reserve(vectorWordsList.size() + mappedWordsList.size()); // make sure we only have a single memory allocation
vectorWordsList.insert(vectorWordsList.end(), mappedWordsList.begin(), mappedWordsList.end());
answered Dec 19 '18 at 15:38
NathanOliverNathanOliver
90.2k15126190
Just use std::vector's assign member function.
//no need to call reserve, bidirectional iterators or better will compute the size and reserve internally.
vectorWordsList.assign(mappedWordsList.begin(), mappedWordsList.end());
If you have existing values in the vector that you don't want overwritten then use insert instead like
vectorWordsList.reserve(vectorWordsList.size() + mappedWordsList.size()); // make sure we only have a single memory allocation
vectorWordsList.insert(vectorWordsList.end(), mappedWordsList.begin(), mappedWordsList.end());
answered Dec 19 '18 at 15:38
NathanOliverNathanOliver
90.2k15126190
edited Dec 20 '18 at 13:39
answered Dec 19 '18 at 15:38
NathanOliverNathanOliver
90.2k15126190
answered Dec 19 '18 at 15:38
NathanOliverNathanOliver
90.2k15126190
answered Dec 19 '18 at 15:38
NathanOliverNathanOliver
90.2k15126190
90.2k15126190
1
I would hope thatassignwould essentiallyreserveinternally.
– François Andrieux
Dec 19 '18 at 15:41
10
@FrançoisAndrieux It most likely would if you passed random access iterators but sincemaphas bidirectional iterators it requires a traversal to known how many elements to allocate space for so it isn't going to do that.
– NathanOliver
Dec 19 '18 at 15:43
1
@NathanOliver libstdc++ actually does essentiallyreserveinternally. For any ForwardIterator, it will callstd::distance, paying for a traversal for anything less than a RandomAccessIterator. You can tracestd::vector::assignto here.
– Justin
Dec 19 '18 at 19:43
1
@Justin Cool. Thanks for finding that. I still like to be explicit, in case other implementations don't do this.
– NathanOliver
Dec 19 '18 at 19:47
Putting a.resize(0)before.reserve()might be an optimization if the elements should be replaced.
– Deduplicator
Dec 19 '18 at 20:46
|
show 2 more comments
1
I would hope thatassignwould essentiallyreserveinternally.
– François Andrieux
Dec 19 '18 at 15:41
10
@FrançoisAndrieux It most likely would if you passed random access iterators but sincemaphas bidirectional iterators it requires a traversal to known how many elements to allocate space for so it isn't going to do that.
– NathanOliver
Dec 19 '18 at 15:43
1
@NathanOliver libstdc++ actually does essentiallyreserveinternally. For any ForwardIterator, it will callstd::distance, paying for a traversal for anything less than a RandomAccessIterator. You can tracestd::vector::assignto here.
– Justin
Dec 19 '18 at 19:43
1
@Justin Cool. Thanks for finding that. I still like to be explicit, in case other implementations don't do this.
– NathanOliver
Dec 19 '18 at 19:47
Putting a.resize(0)before.reserve()might be an optimization if the elements should be replaced.
– Deduplicator
Dec 19 '18 at 20:46
1
1
I would hope that
assign would essentially reserve internally.– François Andrieux
Dec 19 '18 at 15:41
I would hope that
assign would essentially reserve internally.– François Andrieux
Dec 19 '18 at 15:41
10
10
@FrançoisAndrieux It most likely would if you passed random access iterators but since
map has bidirectional iterators it requires a traversal to known how many elements to allocate space for so it isn't going to do that.– NathanOliver
Dec 19 '18 at 15:43
@FrançoisAndrieux It most likely would if you passed random access iterators but since
map has bidirectional iterators it requires a traversal to known how many elements to allocate space for so it isn't going to do that.– NathanOliver
Dec 19 '18 at 15:43
1
1
@NathanOliver libstdc++ actually does essentially
reserve internally. For any ForwardIterator, it will call std::distance, paying for a traversal for anything less than a RandomAccessIterator. You can trace std::vector::assign to here.– Justin
Dec 19 '18 at 19:43
@NathanOliver libstdc++ actually does essentially
reserve internally. For any ForwardIterator, it will call std::distance, paying for a traversal for anything less than a RandomAccessIterator. You can trace std::vector::assign to here.– Justin
Dec 19 '18 at 19:43
1
1
@Justin Cool. Thanks for finding that. I still like to be explicit, in case other implementations don't do this.
– NathanOliver
Dec 19 '18 at 19:47
@Justin Cool. Thanks for finding that. I still like to be explicit, in case other implementations don't do this.
– NathanOliver
Dec 19 '18 at 19:47
Putting a
.resize(0) before .reserve() might be an optimization if the elements should be replaced.– Deduplicator
Dec 19 '18 at 20:46
Putting a
.resize(0) before .reserve() might be an optimization if the elements should be replaced.– Deduplicator
Dec 19 '18 at 20:46
|
show 2 more comments
7
You can use std::copy and std::back_inserter:
std::copy(mappedWordsList.begin(),
mappedWordsList.end(),
std::back_inserter(vectorWordsList));
Honestly, I think that a range-for loop is clearer:
for(const auto& kv : mappedWordsList)
vectorWordsList.emplace_back(kv);
Regardless, you can use std::vector::reserve to preallocate memory on your target vector, avoiding unnecessary reallocations.
answered Dec 19 '18 at 15:35
Vittorio RomeoVittorio Romeo
57.8k17156299
add a comment |
7
You can use std::copy and std::back_inserter:
std::copy(mappedWordsList.begin(),
mappedWordsList.end(),
std::back_inserter(vectorWordsList));
Honestly, I think that a range-for loop is clearer:
for(const auto& kv : mappedWordsList)
vectorWordsList.emplace_back(kv);
Regardless, you can use std::vector::reserve to preallocate memory on your target vector, avoiding unnecessary reallocations.
answered Dec 19 '18 at 15:35
Vittorio RomeoVittorio Romeo
57.8k17156299
add a comment |
7
7
7
You can use std::copy and std::back_inserter:
std::copy(mappedWordsList.begin(),
mappedWordsList.end(),
std::back_inserter(vectorWordsList));
Honestly, I think that a range-for loop is clearer:
for(const auto& kv : mappedWordsList)
vectorWordsList.emplace_back(kv);
Regardless, you can use std::vector::reserve to preallocate memory on your target vector, avoiding unnecessary reallocations.
answered Dec 19 '18 at 15:35
Vittorio RomeoVittorio Romeo
57.8k17156299
You can use std::copy and std::back_inserter:
std::copy(mappedWordsList.begin(),
mappedWordsList.end(),
std::back_inserter(vectorWordsList));
Honestly, I think that a range-for loop is clearer:
for(const auto& kv : mappedWordsList)
vectorWordsList.emplace_back(kv);
Regardless, you can use std::vector::reserve to preallocate memory on your target vector, avoiding unnecessary reallocations.
answered Dec 19 '18 at 15:35
Vittorio RomeoVittorio Romeo
57.8k17156299
edited Dec 19 '18 at 15:36
answered Dec 19 '18 at 15:35
Vittorio RomeoVittorio Romeo
57.8k17156299
answered Dec 19 '18 at 15:35
Vittorio RomeoVittorio Romeo
57.8k17156299
answered Dec 19 '18 at 15:35
Vittorio RomeoVittorio Romeo
57.8k17156299
57.8k17156299
add a comment |
add a comment |
7
It's worth noting that if you are creating a vector for this purpose, you may use the vector's constructor directly:
std::vector<std::pair<FirstType,SecondType>> vectorWordsList( mappedWordsList.begin(), mappedWordsList.end() );
In C++17, you may also omit the vector's template arguments to have the compiler deduce them:
std::vector vectorWordsList( mappedWordsList.begin(), mappedWordsList.end() );
answered Dec 19 '18 at 21:18
Drew DormannDrew Dormann
41.6k979142
Unless you want to create a vector of iterators, you need parens.
– T.C.
Dec 20 '18 at 12:00
@T.C. thank you!
– Drew Dormann
Dec 20 '18 at 16:18
add a comment |
7
It's worth noting that if you are creating a vector for this purpose, you may use the vector's constructor directly:
std::vector<std::pair<FirstType,SecondType>> vectorWordsList( mappedWordsList.begin(), mappedWordsList.end() );
In C++17, you may also omit the vector's template arguments to have the compiler deduce them:
std::vector vectorWordsList( mappedWordsList.begin(), mappedWordsList.end() );
answered Dec 19 '18 at 21:18
Drew DormannDrew Dormann
41.6k979142
Unless you want to create a vector of iterators, you need parens.
– T.C.
Dec 20 '18 at 12:00
@T.C. thank you!
– Drew Dormann
Dec 20 '18 at 16:18
add a comment |
7
7
7
It's worth noting that if you are creating a vector for this purpose, you may use the vector's constructor directly:
std::vector<std::pair<FirstType,SecondType>> vectorWordsList( mappedWordsList.begin(), mappedWordsList.end() );
In C++17, you may also omit the vector's template arguments to have the compiler deduce them:
std::vector vectorWordsList( mappedWordsList.begin(), mappedWordsList.end() );
answered Dec 19 '18 at 21:18
Drew DormannDrew Dormann
41.6k979142
It's worth noting that if you are creating a vector for this purpose, you may use the vector's constructor directly:
std::vector<std::pair<FirstType,SecondType>> vectorWordsList( mappedWordsList.begin(), mappedWordsList.end() );
In C++17, you may also omit the vector's template arguments to have the compiler deduce them:
std::vector vectorWordsList( mappedWordsList.begin(), mappedWordsList.end() );
answered Dec 19 '18 at 21:18
Drew DormannDrew Dormann
41.6k979142
edited Dec 20 '18 at 16:19
answered Dec 19 '18 at 21:18
Drew DormannDrew Dormann
41.6k979142
answered Dec 19 '18 at 21:18
Drew DormannDrew Dormann
41.6k979142
answered Dec 19 '18 at 21:18
Drew DormannDrew Dormann
41.6k979142
41.6k979142
Unless you want to create a vector of iterators, you need parens.
– T.C.
Dec 20 '18 at 12:00
@T.C. thank you!
– Drew Dormann
Dec 20 '18 at 16:18
add a comment |
Unless you want to create a vector of iterators, you need parens.
– T.C.
Dec 20 '18 at 12:00
@T.C. thank you!
– Drew Dormann
Dec 20 '18 at 16:18
Unless you want to create a vector of iterators, you need parens.
– T.C.
Dec 20 '18 at 12:00
Unless you want to create a vector of iterators, you need parens.
– T.C.
Dec 20 '18 at 12:00
@T.C. thank you!
– Drew Dormann
Dec 20 '18 at 16:18
@T.C. thank you!
– Drew Dormann
Dec 20 '18 at 16:18
add a comment |
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1
@Lorand - The sort happens on the
seconditem in the pair, which is not the key.– StoryTeller
Dec 19 '18 at 15:37
1
@Lorand It seems that OP wants to perform the sort based on the values, not the keys.
– ネロク
Dec 19 '18 at 15:38
3
Seems like that question should be flagged as a duplicate of this one, since the answer provided by @NathanOliver is way better than any of the answers to that question. Edit : Though that question includes sorting the result.
– François Andrieux
Dec 19 '18 at 15:40
1
@ALX23z - I agree that
[=]should not be present. But just because it's there doesn't mean everything gets copied. The lambda has to use something from the surrounding scope to capture it.– StoryTeller
Dec 19 '18 at 15:46
1
@ALX23z Actually, it will only copy a variable is you use it in the lambda body. There is no performance penalty to use
[=]if you don't use any of the variables in scope.– NathanOliver
Dec 19 '18 at 15:46