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Integers i.  1 _ _ Index Of

The shape of i.y is |y , and its atoms are the first */|y non-negative integers. A negative element in y causes reversal of the atoms along the corresponding axis. For example:
   i. 5
0 1 2 3 4

   i. 2 _5
4 3 2 1 0
9 8 7 6 5
  If rix is the rank of an item of x, then the shape of the result of x i. y is (-rix)}.$y . Each atom of the result is either #x or the index of the first occurrence among the items of x of the corresponding rix-cell of y .

The comparison in x i. y is tolerant, and fit can be used to specify the tolerance, as in i. !. t .
 


   (i.4);(i._4);(i.2 3 4);(i.2 _3 4);(i.'')
+-------+-------+-----------+-----------+-+
|0 1 2 3|3 2 1 0| 0  1  2  3| 8  9 10 11|0|
|       |       | 4  5  6  7| 4  5  6  7| |
|       |       | 8  9 10 11| 0  1  2  3| |
|       |       |           |           | |
|       |       |12 13 14 15|20 21 22 23| |
|       |       |16 17 18 19|16 17 18 19| |
|       |       |20 21 22 23|12 13 14 15| |
+-------+-------+-----------+-----------+-+

   A=: 'abcdefghijklmnopqrstuvwxyz'
   (A i. 'Now');(A i. 'now');(A {~ A i. 'now')
+--------+--------+---+
|26 14 22|13 14 22|now|
+--------+--------+---+

   m=: 5 4 $ 12{. A
   m;(m i. 'efgh');(1{m);(4{m)
+----+-+----+----+
|abcd|1|efgh|efgh|
|efgh| |    |    |
|ijkl| |    |    |
|abcd| |    |    |
|efgh| |    |    |
+----+-+----+----+



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