Contents
Creating an Empty List
NB. y is anything; result is a list of 0 items, each like y
noneof =: ($0)&(]"0 _)
Culling
Given an array and a predicate, keep only those items for which the predicate is true NB. Adverb. If [x] u y is 1, keep that element of y
usedtocull =: 1 : 'u # ]'
Substring
NB. x is (starting position,length), y is list
NB. result is the selected portion
substr =: (];.0~ ,.)~"1 _
Open a Column
ocol =: >@:({"1)
Select Leading or Trailing Elements, but Not Running Off the End
NB. like {., but limited to the length of y
leading =: ((<. #) {. ])"0 _
NB. like - ux_vy {., but limited to the length of y
trailing =: (-@(<. #) {. ])"0 _
Insert Inside Multilevel Boxed Array
m gives the path, like that used by {::. x is put inside the box at that position in the path. NB. Adverb. Install x in the path given by m
store =: 1 : 0
:
if. #m do. (< x (}.m)store ({.m){::y) ({.m)} y else. x end.
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Apply Verbs on Selected Items
The onitem conjunctions apply u to the cells of y selected my n . There are bivalent, monadic, and dyadic forms. NB. Conjunction. u is verb, n (or [x] v y) is arg to { to select s = desired portion of y
NB. The result of x u s (if dyad) or u s (if monad) replaces s
onitem =: 2 : '(u bivalent (n&{)) n} ]'
onitemm =: 2 : 'n}~ u@:(n&{)'
onitemd =: 2 : '(u (n&{)) n} ]'applyintree applies u at the cell whose path is n . NB. Conjunction. Apply u at the cell indicated by n
applyintree =: 2 : 0
if. #n do. ((u applyintree (}.n)) L:_1 ({.n){y) ({.n)} y else. u y end.
:
NB. The rank is s,0 where s is the surplus of x-rank over y-rank. This causes
NB. the cells of y to be matched up with the largest appropriate blocks x This
NB. is necessary because it is impossible to change the shape of the values being modified
if. #n do. (x u applyintree (}.n) L:_ _1"(0 (,~ >.) x -&(#@$) a) (a =. ({.n){y)) ({.n)} y else. x u y end.
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