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Does the STL have a way to apply a function before calling less than?
Announcing the arrival of Valued Associate #679: Cesar Manara
Planned maintenance scheduled April 17/18, 2019 at 00:00UTC (8:00pm US/Eastern)
The Ask Question Wizard is Live!
Data science time! April 2019 and salary with experienceDoes 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?
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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 5 hours ago
Fomar putesFomar putes
483
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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 5 hours ago
Fomar putesFomar putes
483
New contributor
Fomar putes is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
I don't think this exists, however, it should be very easy to write.
– JVApen
3 hours ago
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 5 hours ago
Fomar putesFomar putes
483
New contributor
Fomar putes is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
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 5 hours ago
Fomar putesFomar putes
483
New contributor
Fomar putes is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 5 hours ago
Fomar putesFomar putes
483
New contributor
Fomar putes is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 5 hours ago
Fomar putesFomar putes
483
New contributor
Fomar putes is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 5 hours ago
Fomar putesFomar putes
483
asked 5 hours ago
Fomar putesFomar putes
483
483
New contributor
Fomar putes is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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New contributor
Fomar putes is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Fomar putes is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
I don't think this exists, however, it should be very easy to write.
– JVApen
3 hours ago
add a comment |
I don't think this exists, however, it should be very easy to write.
– JVApen
3 hours ago
I don't think this exists, however, it should be very easy to write.
– JVApen
3 hours ago
I don't think this exists, however, it should be very easy to write.
– JVApen
3 hours ago
add a comment |
2 Answers
2
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 3 hours ago
Ben Chaliah AyoubBen Chaliah Ayoub
2,422217
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
56 mins ago
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 4 hours ago
Davis HerringDavis Herring
9,1001736
add a comment |
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2 Answers
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oldest
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2 Answers
2
active
oldest
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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 3 hours ago
Ben Chaliah AyoubBen Chaliah Ayoub
2,422217
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
56 mins ago
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 3 hours ago
Ben Chaliah AyoubBen Chaliah Ayoub
2,422217
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
56 mins ago
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 3 hours ago
Ben Chaliah AyoubBen Chaliah Ayoub
2,422217
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 3 hours ago
Ben Chaliah AyoubBen Chaliah Ayoub
2,422217
answered 3 hours ago
Ben Chaliah AyoubBen Chaliah Ayoub
2,422217
answered 3 hours ago
Ben Chaliah AyoubBen Chaliah Ayoub
2,422217
answered 3 hours ago
Ben Chaliah AyoubBen Chaliah Ayoub
2,422217
2,422217
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
56 mins ago
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
56 mins ago
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
56 mins ago
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
56 mins ago
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 4 hours ago
Davis HerringDavis Herring
9,1001736
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 4 hours ago
Davis HerringDavis Herring
9,1001736
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 4 hours ago
Davis HerringDavis Herring
9,1001736
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 4 hours ago
Davis HerringDavis Herring
9,1001736
answered 4 hours ago
Davis HerringDavis Herring
9,1001736
answered 4 hours ago
Davis HerringDavis Herring
9,1001736
answered 4 hours ago
Davis HerringDavis Herring
9,1001736
9,1001736
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
3 hours ago