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digitalmars.D.learn - Selected elements from splitter output

reply Chris Piker <chris hoopjump.com> writes:
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,
May 04 2021
parent reply =?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:
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
May 04 2021
next sibling parent =?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:
On 5/4/21 3:02 PM, Ali =C3=87ehreli 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=20
input range changes how efficient stride() works but we can't say DbI is =

used there.

Ali
May 04 2021
prev sibling parent Chris Piker <chris hoopjump.com> writes:
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.
May 04 2021