groupBy'

lib.groupBy'

Docs pulled from | This Revision | 4 days ago

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

Inputs

op: 1. Function argument
nul: 2. Function argument
pred: 3. Function argument
lst: 4. Function argument

Examples

`lib.lists.groupBy'` usage 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' builtins.add 0 (x: boolToString (x > 2)) [ 5 1 2 3 4 ]
=> { true = 12; false = 3; }

(lib.lists.groupBy')

Noogle detected

Aliases

lib.lists.groupBy'

Implementation

The following is the current implementation of this function.

groupBy' =
    op: nul: pred: lst:
    mapAttrs (name: foldl op nul) (groupBy pred lst);