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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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