## digitalmars.D - Trying Phobos some more

• bearophile (61/61) Feb 12 2014 One way to find what's missing among Phobos ranges and higher
```One way to find what's missing among Phobos ranges and higher
order functions is to try to use them. This is a small
Rosettacode task, given a file of words, it asks to find the
longest pair of anagrams that have not even one letter in the
same position:

http://rosettacode.org/wiki/Anagrams/Deranged_anagrams

I don't fully understand the Clojure solution:

(let
[words    (re-seq #"\w+" (slurp "unixdict.txt"))
anagrams (filter second (vals (group-by sort words)))
deranged (remove #(some true? (apply map = %)) anagrams)]
(prn (last (sort-by #(count (first %)) deranged))))

I have written two D solutions, the first tries to be short and
the second to be faster. This is the first solution (look in that
page for the fast solution):

void main() {
import std.stdio, std.file, std.algorithm, std.string,
std.array;

string[][dstring] anags;
anags[w.array.sort().release.idup] ~= w;

anags
.byValue
.map!(anags => anags.cartesianProduct(anags)
.filter!q{a[].equal!{ a != b }})
.join
.minPos!q{ a[0].length > b[0].length }[0]
.writeln;
}

A better short D version:

void main() {
import std.stdio, std.file, std.algorithm, std.string,
std.array;

"unixdict.txt"
.split
.hashGroupBy!(w => w.sorted.release)
.byValue
.map!(anags => anags
.pairwise
.filter!q{a[].equal!q{ a != b }})
.join
.max!q{ a[0].length }
.writeln;
}

Where:

hashGroupBy returns an associative array of the equivalence
classes, given a key function
(http://d.puremagic.com/issues/show_bug.cgi?id=9842 ).

sorted is similar to an array+sort. But it allocates a new array,
so the its output should be implicitly castable to const
(http://d.puremagic.com/issues/show_bug.cgi?id=5076
https://d.puremagic.com/issues/show_bug.cgi?id=12140 ).

pairwise is a range that yields the pairs, but only the lower
triangle. So it's like two nested loops. In this program it's up
to twice faster than using cartesianProduct
(http://d.puremagic.com/issues/show_bug.cgi?id=6788 ).

max and min accept an optional mapping key function, as in Python
(http://d.puremagic.com/issues/show_bug.cgi?id=4705 ).

Bye,
bearophile
```
Feb 12 2014