From - dyad { (selecting items)

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The dyad { (from) is used to select items from an array. This is sometimes called indexing an array.

   a =. 5 7 9 4 8
   3 { a	NB. select item at index 3
4
   0 { a     	NB. indexes start at 0
5
   2 4 { a 	NB. select 2 items
9 8
   2 0 4 { a	NB. select 3 items
9 5 8

{ selects items from its argument, and therefore selects rows from tables.

   m =. i. 3 4
   m
0 1  2  3
4 5  6  7
8 9 10 11
   0 { m
0 1 2 3
   2 1 { m
8 9 10 11
4 5  6  7

{ selects tables from rank 3 arrays.

   1 { i. 2 3 4
12 13 14 15
16 17 18 19
20 21 22 23

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