Removing an element from a list or array
I feel dumb. I've been searching for how to do this, and each page or forum entry I read makes me more confused. Let's say I have a list of values (Monday, Tuesday, Wednesday, Thursday, Friday). I can store this list in an Slist, Dlist, Array etc -- any collection is fine. I decide I want to remove Thursday from the list. How? I see that linearRemove is meant to do this, but that takes a range. How do I get a range of 'Thursday'?
Re: Removing an element from a list or array
On Wednesday, 6 August 2014 at 19:01:26 UTC, Patrick wrote:
I feel dumb. I've been searching for how to do this, and each
page or forum entry I read makes me more confused.
Let's say I have a list of values (Monday, Tuesday, Wednesday,
Thursday, Friday). I can store this list in an Slist, Dlist,
Array etc -- any collection is fine.
I decide I want to remove Thursday from the list.
How? I see that linearRemove is meant to do this, but that
takes a range. How do I get a range of 'Thursday'?
Slicing a container gives you a range for that container, and
it's that type that needs to be used to remove elements (either
that, or that type wrapped with std.range.Take), since otherwise,
the container wouldn't know which elements you were trying to
remove - just their values.
You need to use std.algorithm.find to find the element that you
want to remove, in which case, you have a range starting at that
element (but it contains everything after it too). So, you used
std.range.take to take the number of elements that you want from
the range, and then you pass that result to linearRemove. e.g.
import std.algorithm;
import std.container;
import std.range;
void main()
{
auto arr = Array!string(Monday, Tuesday, Wednesday,
Thursday, Friday);
auto range = arr[];
assert(equal(range, [Monday, Tuesday, Wednesday,
Thursday, Friday]));
auto found = range.find(Thursday);
assert(equal(found, [Thursday, Friday]));
arr.linearRemove(found.take(1));
assert(equal(arr[], [Monday, Tuesday, Wednesday,
Friday]));
}
C++ does it basically the same way that D does, but it's actually
one place where iterators are cleaner, because you can just pass
the iterator to erase, whereas with a range, that would remove
all of the elements after that element, which is why you need
take, which makes it that much more complicated.
Using opSlice like that along with range-based functions like
find which don't return a new range type will always be what
you'll need to do in the general case, but it would definitely be
nice if we added functions like removeFirst to remove elements
which matched a specific value so that the simple use cases
didn't require using find.
- Jonathan M Davis
Re: Removing an element from a list or array
Thank you, that is a great sample.
On Wednesday, 6 August 2014 at 19:41:50 UTC, Jonathan M Davis
wrote:
On Wednesday, 6 August 2014 at 19:01:26 UTC, Patrick wrote:
I feel dumb. I've been searching for how to do this, and each
page or forum entry I read makes me more confused.
Let's say I have a list of values (Monday, Tuesday, Wednesday,
Thursday, Friday). I can store this list in an Slist, Dlist,
Array etc -- any collection is fine.
I decide I want to remove Thursday from the list.
How? I see that linearRemove is meant to do this, but that
takes a range. How do I get a range of 'Thursday'?
Slicing a container gives you a range for that container, and
it's that type that needs to be used to remove elements (either
that, or that type wrapped with std.range.Take), since
otherwise, the container wouldn't know which elements you were
trying to remove - just their values.
You need to use std.algorithm.find to find the element that you
want to remove, in which case, you have a range starting at
that element (but it contains everything after it too). So, you
used std.range.take to take the number of elements that you
want from the range, and then you pass that result to
linearRemove. e.g.
import std.algorithm;
import std.container;
import std.range;
void main()
{
auto arr = Array!string(Monday, Tuesday, Wednesday,
Thursday, Friday);
auto range = arr[];
assert(equal(range, [Monday, Tuesday, Wednesday,
Thursday, Friday]));
auto found = range.find(Thursday);
assert(equal(found, [Thursday, Friday]));
arr.linearRemove(found.take(1));
assert(equal(arr[], [Monday, Tuesday, Wednesday,
Friday]));
}
C++ does it basically the same way that D does, but it's
actually one place where iterators are cleaner, because you can
just pass the iterator to erase, whereas with a range, that
would remove all of the elements after that element, which is
why you need take, which makes it that much more complicated.
Using opSlice like that along with range-based functions like
find which don't return a new range type will always be what
you'll need to do in the general case, but it would definitely
be nice if we added functions like removeFirst to remove
elements which matched a specific value so that the simple use
cases didn't require using find.
- Jonathan M Davis
