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Does the STL have a way to apply a function before calling less than?
Does the 'mutable' keyword have any purpose other than allowing the variable to be modified by a const function?Pretty-print C++ STL containersElegant way to find closest value in a vector from aboveLess-than function dereferencing pointersShould custom containers have free begin/end functions?why do std::sort and partial_sort require random-access iterators?c++ Sort Vector based on distance to external PointHow can I avoid “for” loops with an “if” condition inside them with C++?Do STL algorithms functions, like accumulate, avoid copy if the function passed to them accepts a reference?Why does std::sort segfault with non-transitive comparators?
.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty height:90px;width:728px;box-sizing:border-box;
A lot of algorithms accept a comparison object. Often, I end up with something like
std::sort(begin, end, [&](auto const& lhs, auto const& rhs)
return Function(lhs) < Function(rhs);
);
Is there anything in the STL to apply a Function before calling less than? So I could write:
std::sort(begin, end, std::DoesThisExist(Function));
I know I could write my own, but I wonder if this already exists. I glanced through cpprefence but didn't see it. Could easily have missed it.
c++
asked Apr 14 at 17:59
Fomar putesFomar putes
534
add a comment |
A lot of algorithms accept a comparison object. Often, I end up with something like
std::sort(begin, end, [&](auto const& lhs, auto const& rhs)
return Function(lhs) < Function(rhs);
);
Is there anything in the STL to apply a Function before calling less than? So I could write:
std::sort(begin, end, std::DoesThisExist(Function));
I know I could write my own, but I wonder if this already exists. I glanced through cpprefence but didn't see it. Could easily have missed it.
c++
asked Apr 14 at 17:59
Fomar putesFomar putes
534
I don't think this exists, however, it should be very easy to write.
– JVApen
Apr 14 at 20:03
std::bind, see details below
– Helmut Zeisel
Apr 16 at 7:24
add a comment |
A lot of algorithms accept a comparison object. Often, I end up with something like
std::sort(begin, end, [&](auto const& lhs, auto const& rhs)
return Function(lhs) < Function(rhs);
);
Is there anything in the STL to apply a Function before calling less than? So I could write:
std::sort(begin, end, std::DoesThisExist(Function));
I know I could write my own, but I wonder if this already exists. I glanced through cpprefence but didn't see it. Could easily have missed it.
c++
asked Apr 14 at 17:59
Fomar putesFomar putes
534
A lot of algorithms accept a comparison object. Often, I end up with something like
std::sort(begin, end, [&](auto const& lhs, auto const& rhs)
return Function(lhs) < Function(rhs);
);
Is there anything in the STL to apply a Function before calling less than? So I could write:
std::sort(begin, end, std::DoesThisExist(Function));
I know I could write my own, but I wonder if this already exists. I glanced through cpprefence but didn't see it. Could easily have missed it.
c++
c++
asked Apr 14 at 17:59
Fomar putesFomar putes
534
asked Apr 14 at 17:59
Fomar putesFomar putes
534
asked Apr 14 at 17:59
Fomar putesFomar putes
534
asked Apr 14 at 17:59
Fomar putesFomar putes
534
asked Apr 14 at 17:59
Fomar putesFomar putes
534
534
I don't think this exists, however, it should be very easy to write.
– JVApen
Apr 14 at 20:03
std::bind, see details below
– Helmut Zeisel
Apr 16 at 7:24
add a comment |
I don't think this exists, however, it should be very easy to write.
– JVApen
Apr 14 at 20:03
std::bind, see details below
– Helmut Zeisel
Apr 16 at 7:24
I don't think this exists, however, it should be very easy to write.
– JVApen
Apr 14 at 20:03
I don't think this exists, however, it should be very easy to write.
– JVApen
Apr 14 at 20:03
std::bind, see details below
– Helmut Zeisel
Apr 16 at 7:24
std::bind, see details below
– Helmut Zeisel
Apr 16 at 7:24
add a comment |
3 Answers
3
active
oldest
votes
The STL should have a sort that works on a transform of the elements rather than the elements themselves. The reason for this being that Function could actually be costly. By simply incorporating it into the comparison as you did you invoke Function nlog(n) times rather than the optimal n.
To sort arrays in parallel using STL algorithm :
std::sort(std::execution::par, container.begin(), container.end(), comparison_object);
Anyway, I think if you try to just sort with ranges::view::transform it will probably still call your function ~n log n many times. But you could just do something like:
auto values = /* some container */;
auto keys = values | ranges::view::transform(f) | ranges::to_vector;
ranges::sort(ranges::view::zip(keys, values),
[](auto const& x, auto const& y) return std::get<0>(x) < std::get<0>(y); );
answered Apr 14 at 19:59
Ben Chaliah AyoubBen Chaliah Ayoub
4,532422
Calling a transform n log n times matters only if its expense is significant compared to the comparison and permutation. In common cases where the “transform” is just selecting a member or performing simple arithmetic, allocating the space for the key values would be much worse than the repeated work.
– Davis Herring
Apr 14 at 22:10
add a comment |
The Ranges TS (which has been merged for C++20) defines variations of many of the standard algorithms that include projections with exactly this behavior.
answered Apr 14 at 18:11
Davis HerringDavis Herring
10.8k1736
add a comment |
In principle, you could use std::bind, but it is very verbose:
typedef std::remove_reference<decltype(*begin)>::type T;
std::sort(begin, end, std::bind(std::less<T>(),
std::bind(Function,std::placeholders::_1),
std::bind(Function,std::placeholders::_2)));
answered Apr 15 at 8:32
Helmut ZeiselHelmut Zeisel
1387
add a comment |
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3 Answers
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3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
The STL should have a sort that works on a transform of the elements rather than the elements themselves. The reason for this being that Function could actually be costly. By simply incorporating it into the comparison as you did you invoke Function nlog(n) times rather than the optimal n.
To sort arrays in parallel using STL algorithm :
std::sort(std::execution::par, container.begin(), container.end(), comparison_object);
Anyway, I think if you try to just sort with ranges::view::transform it will probably still call your function ~n log n many times. But you could just do something like:
auto values = /* some container */;
auto keys = values | ranges::view::transform(f) | ranges::to_vector;
ranges::sort(ranges::view::zip(keys, values),
[](auto const& x, auto const& y) return std::get<0>(x) < std::get<0>(y); );
answered Apr 14 at 19:59
Ben Chaliah AyoubBen Chaliah Ayoub
4,532422
Calling a transform n log n times matters only if its expense is significant compared to the comparison and permutation. In common cases where the “transform” is just selecting a member or performing simple arithmetic, allocating the space for the key values would be much worse than the repeated work.
– Davis Herring
Apr 14 at 22:10
add a comment |
The STL should have a sort that works on a transform of the elements rather than the elements themselves. The reason for this being that Function could actually be costly. By simply incorporating it into the comparison as you did you invoke Function nlog(n) times rather than the optimal n.
To sort arrays in parallel using STL algorithm :
std::sort(std::execution::par, container.begin(), container.end(), comparison_object);
Anyway, I think if you try to just sort with ranges::view::transform it will probably still call your function ~n log n many times. But you could just do something like:
auto values = /* some container */;
auto keys = values | ranges::view::transform(f) | ranges::to_vector;
ranges::sort(ranges::view::zip(keys, values),
[](auto const& x, auto const& y) return std::get<0>(x) < std::get<0>(y); );
answered Apr 14 at 19:59
Ben Chaliah AyoubBen Chaliah Ayoub
4,532422
Calling a transform n log n times matters only if its expense is significant compared to the comparison and permutation. In common cases where the “transform” is just selecting a member or performing simple arithmetic, allocating the space for the key values would be much worse than the repeated work.
– Davis Herring
Apr 14 at 22:10
add a comment |
The STL should have a sort that works on a transform of the elements rather than the elements themselves. The reason for this being that Function could actually be costly. By simply incorporating it into the comparison as you did you invoke Function nlog(n) times rather than the optimal n.
To sort arrays in parallel using STL algorithm :
std::sort(std::execution::par, container.begin(), container.end(), comparison_object);
Anyway, I think if you try to just sort with ranges::view::transform it will probably still call your function ~n log n many times. But you could just do something like:
auto values = /* some container */;
auto keys = values | ranges::view::transform(f) | ranges::to_vector;
ranges::sort(ranges::view::zip(keys, values),
[](auto const& x, auto const& y) return std::get<0>(x) < std::get<0>(y); );
answered Apr 14 at 19:59
Ben Chaliah AyoubBen Chaliah Ayoub
4,532422
The STL should have a sort that works on a transform of the elements rather than the elements themselves. The reason for this being that Function could actually be costly. By simply incorporating it into the comparison as you did you invoke Function nlog(n) times rather than the optimal n.
To sort arrays in parallel using STL algorithm :
std::sort(std::execution::par, container.begin(), container.end(), comparison_object);
Anyway, I think if you try to just sort with ranges::view::transform it will probably still call your function ~n log n many times. But you could just do something like:
auto values = /* some container */;
auto keys = values | ranges::view::transform(f) | ranges::to_vector;
ranges::sort(ranges::view::zip(keys, values),
[](auto const& x, auto const& y) return std::get<0>(x) < std::get<0>(y); );
answered Apr 14 at 19:59
Ben Chaliah AyoubBen Chaliah Ayoub
4,532422
answered Apr 14 at 19:59
Ben Chaliah AyoubBen Chaliah Ayoub
4,532422
answered Apr 14 at 19:59
Ben Chaliah AyoubBen Chaliah Ayoub
4,532422
answered Apr 14 at 19:59
Ben Chaliah AyoubBen Chaliah Ayoub
4,532422
4,532422
Calling a transform n log n times matters only if its expense is significant compared to the comparison and permutation. In common cases where the “transform” is just selecting a member or performing simple arithmetic, allocating the space for the key values would be much worse than the repeated work.
– Davis Herring
Apr 14 at 22:10
add a comment |
Calling a transform n log n times matters only if its expense is significant compared to the comparison and permutation. In common cases where the “transform” is just selecting a member or performing simple arithmetic, allocating the space for the key values would be much worse than the repeated work.
– Davis Herring
Apr 14 at 22:10
Calling a transform n log n times matters only if its expense is significant compared to the comparison and permutation. In common cases where the “transform” is just selecting a member or performing simple arithmetic, allocating the space for the key values would be much worse than the repeated work.
– Davis Herring
Apr 14 at 22:10
Calling a transform n log n times matters only if its expense is significant compared to the comparison and permutation. In common cases where the “transform” is just selecting a member or performing simple arithmetic, allocating the space for the key values would be much worse than the repeated work.
– Davis Herring
Apr 14 at 22:10
add a comment |
The Ranges TS (which has been merged for C++20) defines variations of many of the standard algorithms that include projections with exactly this behavior.
answered Apr 14 at 18:11
Davis HerringDavis Herring
10.8k1736
add a comment |
The Ranges TS (which has been merged for C++20) defines variations of many of the standard algorithms that include projections with exactly this behavior.
answered Apr 14 at 18:11
Davis HerringDavis Herring
10.8k1736
add a comment |
The Ranges TS (which has been merged for C++20) defines variations of many of the standard algorithms that include projections with exactly this behavior.
answered Apr 14 at 18:11
Davis HerringDavis Herring
10.8k1736
The Ranges TS (which has been merged for C++20) defines variations of many of the standard algorithms that include projections with exactly this behavior.
answered Apr 14 at 18:11
Davis HerringDavis Herring
10.8k1736
answered Apr 14 at 18:11
Davis HerringDavis Herring
10.8k1736
answered Apr 14 at 18:11
Davis HerringDavis Herring
10.8k1736
answered Apr 14 at 18:11
Davis HerringDavis Herring
10.8k1736
10.8k1736
add a comment |
add a comment |
In principle, you could use std::bind, but it is very verbose:
typedef std::remove_reference<decltype(*begin)>::type T;
std::sort(begin, end, std::bind(std::less<T>(),
std::bind(Function,std::placeholders::_1),
std::bind(Function,std::placeholders::_2)));
answered Apr 15 at 8:32
Helmut ZeiselHelmut Zeisel
1387
add a comment |
In principle, you could use std::bind, but it is very verbose:
typedef std::remove_reference<decltype(*begin)>::type T;
std::sort(begin, end, std::bind(std::less<T>(),
std::bind(Function,std::placeholders::_1),
std::bind(Function,std::placeholders::_2)));
answered Apr 15 at 8:32
Helmut ZeiselHelmut Zeisel
1387
add a comment |
In principle, you could use std::bind, but it is very verbose:
typedef std::remove_reference<decltype(*begin)>::type T;
std::sort(begin, end, std::bind(std::less<T>(),
std::bind(Function,std::placeholders::_1),
std::bind(Function,std::placeholders::_2)));
answered Apr 15 at 8:32
Helmut ZeiselHelmut Zeisel
1387
In principle, you could use std::bind, but it is very verbose:
typedef std::remove_reference<decltype(*begin)>::type T;
std::sort(begin, end, std::bind(std::less<T>(),
std::bind(Function,std::placeholders::_1),
std::bind(Function,std::placeholders::_2)));
answered Apr 15 at 8:32
Helmut ZeiselHelmut Zeisel
1387
answered Apr 15 at 8:32
Helmut ZeiselHelmut Zeisel
1387
answered Apr 15 at 8:32
Helmut ZeiselHelmut Zeisel
1387
answered Apr 15 at 8:32
Helmut ZeiselHelmut Zeisel
1387
1387
add a comment |
add a comment |
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I don't think this exists, however, it should be very easy to write.
– JVApen
Apr 14 at 20:03
std::bind, see details below
– Helmut Zeisel
Apr 16 at 7:24