Dne 14.3.2017 v 16:02 Russel Winder via Digitalmars-d-learn napsal(a):

> I am having a hard time Google-ing today. Pytho, Groovy, Kotlin, etc.
> have a "groupBy" function that takes a sequence and a key and creates a
> dictionary/associative array with keys the result of the key function
> on the sequence and key values all the items that match the key.
>
> D doesn't seem to have such a function directly. Unless I missed it…
Can you post some example? Maybe in python, kotlin whatever so I can better understand what you want

On Tue, 2017-03-14 at 16:12 +0100, Daniel Kozak via Digitalmars-d-learn wrote:
> […]
> 
> Can you post some example? Maybe in python, kotlin whatever so I can better understand what you want

In my head I had something such as Groovy's

  files = new File('test-data').listFiles().collect{it.name}
  println files.groupBy({ it.split('_')[0]})


The I remembered that itertools.groupby in Python behaves like D's std.algorithm.iteration.chunkBy and not like Groovy's groupBy. So in Python you have to hack it with:

  from collections import defaultdict
  from os import listdir
  from os.path import isfile, splitext

  result = defaultdict(list)
  files = tuple((item.split('_')[0], item) for item in listdir('test-data') if isfile('test-data/' + item))
  for p, v in files:
    result[p] += [v]
  print(result)

Given the seeming lack of Groovy-style groupBy, I guess I will have to do something Python-like in D. Except I am not sure D has an equivalent of defaultdict.

-- 
Russel. ============================================================================= Dr Russel Winder      t: +44 20 7585 2200   voip: sip:russel.winder@ekiga.net 41 Buckmaster Road    m: +44 7770 465 077   xmpp: russel@winder.org.uk London SW11 1EN, UK   w: www.russel.org.uk  skype: russel_winder

On Tue, 2017-03-14 at 16:35 +0000, Russel Winder wrote:
> 

So by analogy with the Python code I get the following D code, but it seems ugly compared to the niceness of the Groovy code (and equivalent Kotlin and Ceylon codes):

import std.array: array, split;
import std.algorithm: filter, map;
import std.file: dirEntries, SpanMode;
import std.path: baseName, dirName;
import std.stdio: writeln;
import std.typecons: Tuple, tuple;


	auto files = dirEntries(path, SpanMode.shallow)
	 .filter!(a => a.isFile)
	 .map!(a => a.baseName)
	 .map!(a => tuple(a.split('_')[0], a))
	 .array;
	writeln(files);
	string[][string] groups;
	foreach (Tuple!(string, string) f; files) {
		groups[f[0]] ~= [f[1]];
	}



-- 
Russel. ============================================================================= Dr Russel Winder      t: +44 20 7585 2200   voip: sip:russel.winder@ekiga.net 41 Buckmaster Road    m: +44 7770 465 077   xmpp: russel@winder.org.uk London SW11 1EN, UK   w: www.russel.org.uk  skype: russel_winder