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Add group-by and partition-by to the core.

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Semantics are mostly emulated from Clojure.
This commit is contained in:
Calvin Rose 2021-03-04 19:34:36 -06:00
parent 6392b37c47
commit c9097623d6
1 changed files with 30 additions and 0 deletions
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30
src/boot/boot.janet
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@ -1451,6 +1451,36 @@
(set (freqs x) (if n (+ 1 n) 1))) (set (freqs x) (if n (+ 1 n) 1)))
freqs) freqs)
(defn group-by
``Group elements of `ind` by a function `f` and put the results into a table. The keys of
the table are the distinct return values of `f`, and the values are arrays of all elements of `ind`
that are equal to that value.``
[f ind]
(def ret @{})
(each x ind
(def y (f x))
(if-let [arr (get ret y)]
(array/push arr x)
(put ret y @[x])))
ret)
(defn partition-by
``Partition elements of a sequential data structure by a representative function `f`. Partitions
split when `(f x)` changes values when iterating to the next element `x` of `ind`. Returns a new array
of arrays.``
[f ind]
(def ret @[])
(var span nil)
(var category nil)
(var is-new true)
(each x ind
(def y (f x))
(cond
is-new (do (set is-new false) (set category y) (set span @[x]) (array/push ret span))
(= y category) (array/push span x)
(do (set category y) (set span @[x]) (array/push ret span))))
ret)
(defn interleave (defn interleave
"Returns an array of the first elements of each col, then the second, etc." "Returns an array of the first elements of each col, then the second, etc."
[& cols] [& cols]