lib: add groupBy (#38612)

This commit is contained in:
volth 2018-06-10 17:31:09 +00:00 committed by xeji
parent 95a8cb3ade
commit 4e85c4ff27
2 changed files with 37 additions and 1 deletions

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@ -76,7 +76,7 @@ let
optional optionals toList range partition zipListsWith zipLists
reverseList listDfs toposort sort naturalSort compareLists take
drop sublist last init crossLists unique intersectLists
subtractLists mutuallyExclusive;
subtractLists mutuallyExclusive groupBy groupBy';
inherit (strings) concatStrings concatMapStrings concatImapStrings
intersperse concatStringsSep concatMapStringsSep
concatImapStringsSep makeSearchPath makeSearchPathOutput

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@ -250,6 +250,42 @@ rec {
else { right = t.right; wrong = [h] ++ t.wrong; }
) { right = []; wrong = []; });
/* Splits the elements of a list into many lists, using the return value of a predicate.
Predicate should return a string which becomes keys of attrset `groupBy' returns.
`groupBy'' allows to customise the combining function and initial value
Example:
groupBy (x: boolToString (x > 2)) [ 5 1 2 3 4 ]
=> { true = [ 5 3 4 ]; false = [ 1 2 ]; }
groupBy (x: x.name) [ {name = "icewm"; script = "icewm &";}
{name = "xfce"; script = "xfce4-session &";}
{name = "icewm"; script = "icewmbg &";}
{name = "mate"; script = "gnome-session &";}
]
=> { icewm = [ { name = "icewm"; script = "icewm &"; }
{ name = "icewm"; script = "icewmbg &"; } ];
mate = [ { name = "mate"; script = "gnome-session &"; } ];
xfce = [ { name = "xfce"; script = "xfce4-session &"; } ];
}
groupBy' allows to customise the combining function and initial value
Example:
groupBy' builtins.add 0 (x: boolToString (x > 2)) [ 5 1 2 3 4 ]
=> { true = 12; false = 3; }
*/
groupBy' = op: nul: pred: lst:
foldl' (r: e:
let
key = pred e;
in
r // { ${key} = op (r.${key} or nul) e; }
) {} lst;
groupBy = groupBy' (sum: e: sum ++ [e]) [];
/* Merges two lists of the same size together. If the sizes aren't the same
the merging stops at the shortest. How both lists are merged is defined
by the first argument.