Symbol Take
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↑ — Take symbol — Keystroke(usually) ALT+y ; Character (⎕UCS) 8593
Usage
Dyadic function A↑B - where A is the number of elements to take and B is the vector or array to operate on. Take first(A is positive) n or last(A is negative) n elements of an array. Take and Rho share a similar property - the left argument specifies the size of the resultant array.
Examples
5↑1 ⍝Take the first 5 elements, given scalar integer 1
1 0 0 0 0 ⍝Result creates a vector of 5 elements, since only a single scalar was present, 4 additional zeroes are appended to the vector.
¯4↑45 78 33 99 10 11 12 13 ⍝Take the last 4 elements, given a vector of 8 integers
10 11 12 13 ⍝APL/NARS Interpreter returns the last 4 elements, a vector.
¯5↑'abcdefghijklmnop'
lmnop ⍝Result is the last 5 elements from the alphabet sub-string(take's right argument), result is similarly a string.
A←3 4⍴⍳12 ⍝Store a 3-row by 4-column matrix of the set of integers from 1 through 12 in variable A
A ⍝Display the contents of variable A, which has 3 rows and 4 columns of consecutive integers:
1 2 3 4
5 6 7 8
9 10 11 12
2 3↑A ⍝Take just the FIRST 2 rows and 3 columns of variable A, display the requested results:
1 2 3
5 6 7
¯2 3↑A ⍝Take the LAST 2 rows and FIRST 3 columns of variable A, display the results:
5 6 7
9 10 11
4 5↑A ⍝Take 4 rows and 5 columns of variable A, ZEROES are APPENDED when left arguments exceed array sizes of a NUMERIC matrix.
1 2 3 4 0
5 6 7 8 0
9 10 11 12 0
0 0 0 0 0
¯4 ¯5↑A ⍝Take negative 4 rows and negative 5 cols of variable A. Result: ZEROES are PREFIXED onto numeric matrix A:
0 0 0 0 0
0 1 2 3 4
0 5 6 7 8
0 9 10 11 12
See Also
- Rho: ⍴ especially Dyadic rho and it's leftmost argument
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