Hi D

I have a white-space delimited file with quite a few columns, but I only care about columns 0, 2, 3, 4, 8, 9, 10.  Since I don't need most of the 60+ columns it seemed like:

   std.algorithm.iteration.splitter()

would be a better function to use then std.array.split().  My problem is that I don't know how to get the elements I care about from the splitter, for example:

char[] line;
char[][] cols_needed;
while(file.readln(line)){
   auto a = line.splitter()
   cols_needed = ???
}

On a related note, are there any standard library functions that select specific elements of a range by index without a loop?  So the logical equivalent of:

auto string_range
char[][] wanted = string_range.get( [1, 5, 7] );  // pseudo-code element selection

It's not a big deal if there's not something standard.

Thanks for the help,

On 5/4/21 1:40 PM, Chris Piker wrote:

> I only care about columns 0, 2, 3, 4, 8, 9, 10.

That's std.range.stride.

> char[][] wanted = string_range.get( [1, 5, 7] );  // pseudo-code element

That's std.range.indexed.

import std.range;
import std.stdio;

void main() {
  auto r = 10.iota.stride(2);
  writeln(r);

  writeln(r.indexed([1, 3]));

  // Note: The above works only because 'stride' applies
  // "design by introspection" (DbI) and is able to work as a
  // RandomAccessRanges. Not every range can do that; so, in a more
  // general case, you would have to turn your range to a
  // RandomAccessRange by calling std.array.array first:
  auto r2 = r.array;
  // The following can work with any InputRange only after doing that.
  writeln(r2.indexed([1, 3]));
}

Ali

On 5/4/21 3:02 PM, Ali Çehreli wrote:

>    // Note: The above works only because 'stride' applies
>    // "design by introspection" (DbI) and is able to work as a
>    // RandomAccessRanges.

Ok, I was too enthusiastic there. The RandomAccessRange'ness of the input range changes how efficient stride() works but we can't say DbI is used there.

Ali

On Tuesday, 4 May 2021 at 22:02:11 UTC, Ali Çehreli wrote:
> On 5/4/21 1:40 PM, Chris Piker wrote:
>
> > I only care about columns 0, 2, 3, 4, 8, 9, 10.
>
> That's std.range.stride.
>
> > char[][] wanted = string_range.get( [1, 5, 7] );  //
> pseudo-code element
>
> That's std.range.indexed.

Hey Thanks!

And even more, thanks for the book.  It's very well organized.  I keep a paper copy of "Programming in D" open on my desk all the time these days.  Looking forward to getting a few copies for work once we're back in the office.