how use lowerBound with just sorting key, not complete values

[Daniel Davidson]

On Tuesday, 12 November 2013 at 16:34:30 UTC, bearophile wrote:
> Daniel Davidson:
>
>> Yes, but that is only giving the dates. I want the actual 
>> array elements. Suppose S is a large object with lots of extra 
>> fields in addition to `string foo`. There should be a way to 
>> pull out the lower bound based on a date without creating a 
>> needle (S). Maybe lowerBound is not the right function?
>
> Second try:
>
> import std.stdio, std.range, std.datetime, std.algorithm,
>        std.array, std.typecons;
>
> struct S {
>     Date date;
>     string foo;
> }
>
> void main() {
>     auto sarr = [S(Date(2000, 1, 1), "x"),
>                  S(Date(2000, 2, 1), "a"),
>                  S(Date(2000, 3, 1), "foo")];
>     assert(sarr.isSorted!q{ a.date < b.date });
>
>     sarr.writeln;
>     auto needle = S(Date(2000, 2, 1));
>
>     sarr
>     .map!(s => s.date)
>     .zip(sarr.length.iota)
>     .assumeSorted!q{ a[0] < b[0] }
>     .lowerBound(tuple(needle.date, 0))
>     .map!(p => sarr[p[1]])
>     .writeln;
> }
>
>
> Output:
>
> [S(2000-Jan-01, "x"), S(2000-Feb-01, "a"), S(2000-Mar-01, 
> "foo")]
> [S(2000-Jan-01, "x")]
>
> Bye,
> bearophile

Well, I think that is it. Thanks, bearophile!

Pardon the redirect, but while you are at it, I would appreciate 
your take on this one 
(http://forum.dlang.org/post/gofijmqwhfcwgbruzkvz@forum.dlang.org). 
I'm sure you'll improve it and teach me a few things on the way 
;-)

Thanks
Dan