[Pharo-users] [ANN] Grouper

Julien Delplanque julien.delplanque at inria.fr
Mon Dec 9 09:08:53 EST 2019


Hello,

I made a small library that reify grouping (that one does via #groupBy: 
usually): Grouper https://github.com/juliendelplanque/Grouper

It is designed in the same spirit as SortFunction, but for grouping.

Quick example:

The following code snippet using Grouper:

(10  to:  50)groupUsing:  [:integer  | integer asString first ].
"an OrderedDictionary(
$1->#(10 11 12 13 14 15 16 17 18 19)
$2->#(20 21 22 23 24 25 26 27 28 29)
$3->#(30 31 32 33 34 35 36 37 38 39)
$4->#(40 41 42 43 44 45 46 47 48 49)
$5->#(50))"

is equivalent to the following code snippet using 
built-in|#groupedBy:|method:

(10  to:  50)groupedBy:  [:integer  | integer asString first ]
"an OrderedDictionary(
$1->#(10 11 12 13 14 15 16 17 18 19)
$2->#(20 21 22 23 24 25 26 27 28 29)
$3->#(30 31 32 33 34 35 36 37 38 39)
$4->#(40 41 42 43 44 45 46 47 48 49)
$5->#(50))"

The advantage of using it is that it allows one to compose grouper objects.

Thus, it is easy to describe grouping on 2 or 3 levels.

Fore example:

The power of Grouper is that group description are first-class objects. 
Thus, it is possible to compose group descriptions in order to group a 
flat collection on multiple levels.

For example:

groupComposition:=  [:integer  | integer asString first ] grouper , [:integer  | integer asString second ].
(10  to:  50)groupUsing:  groupComposition.
"an OrderedDictionary(
$1->an OrderedDictionary(
$0->#(10) $1->#(11) $2->#(12) $3->#(13) $4->#(14) $5->#(15) $6->#(16) 
$7->#(17) $8->#(18) $9->#(19))
$2->an OrderedDictionary(
$0->#(20) $1->#(21) $2->#(22) $3->#(23) $4->#(24) $5->#(25) $6->#(26) 
$7->#(27) $8->#(28) $9->#(29))
$3->an OrderedDictionary(
$0->#(30) $1->#(31) $2->#(32) $3->#(33) $4->#(34) $5->#(35) $6->#(36) 
$7->#(37) $8->#(38) $9->#(39))
$4->an OrderedDictionary(
$0->#(40) $1->#(41) $2->#(42) $3->#(43) $4->#(44) $5->#(45) $6->#(46) 
$7->#(47) $8->#(48) $9->#(49))
$5->an OrderedDictionary($0->#(50)))"

On the github, there are more example showing how to build trees with 
custom objects.

Any feedback for this library is welcome.

I would like to propose it to Pharo in the near future because it would 
simplify a lot of code in DrTests (related to result tree views, the 
tree on the right of the UI).

I don't know if it will be possible before next release as we are in 
feature freeze.

Cheers,

Julien

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