Vocabulary/squarert

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] y

Same

Rank Infinity -- operates on x and y as a whole -- WHY IS THIS IMPORTANT?

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Returns noun y unchanged, i.e. (]y) is equivalent to y.

   z=: i.6           NB. try any noun here
   assert z -: ]z

NOTE: Same ([ y) is equivalent to (] y).

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Common uses

1. Use in the J session to both display a noun and assign it to a name with a single sentence

   ] z=: i:2
_2 _1 0 1 2

2. In a train of verbs, refer to the argument of the train

   (2 { ]) 3 1 4 1 5 9
4

When ] is executed, it is replaced by the value of its argument, which is the argument of the train (2 { ])

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Related Primitives

Same ([ y)

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Use These Combinations

Combinations using ] y that have exceptionally good performance include:

What it does	Type; Precisions; Ranks	Syntax	Variants; Restrictions	Benefits; Bug Warnings
Extract substring/subarray	table or list	x ];.0 y	or [;.0	avoids creating indexes
Translate characters from q to p	byte	(p {~ q i. ]) y	also ((q i.]) { p"_) y and (q&i. { p"_) y
Reshape infixes		x ]\ y	[ , in place of ]

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x ] y

Right

Rank Infinity -- operates on x and y as a whole -- WHY IS THIS IMPORTANT?

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Returns the (noun) value of y -- ignoring x

   x=: 3
   y=: 5
   x ] y
5
   assert y -: x ] y   NB. try with any 2 nouns as x and y

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Common uses

1. Separate two (numeric) atoms to prevent J treating them as a single noun (list)

   i."0   3 4 5
|length error
   i."0  ] 3 4 5       NB. need to separate the 0 3 4 5
0 1 2 0 0
0 1 2 3 0
0 1 2 3 4
   ;: 'i."0   3 4 5'   NB. see, they were treated as one word
+--+-+---------+
|i.|"|0   3 4 5|
+--+-+---------+

2. Use with a conjunction or adverb where the identity verb suffices to yield the behavior required

   _3 ]\ 1 0 0   0 1 0    0 0 1
1 0 0
0 1 0
0 0 1

3. In a tacit verb (monad or dyad): use  ] (and  [) to bring in the value(s) of argument(s) y (and x)

   13 : 'x+(x-y)*y'    NB. converts code string to a tacit verb
[ + - * ]

4. In a dyadic tacit verb: use u@] to execute u on the y-argument of the verb

   3 (< , <) 'a'       NB. No good: the < are executed as dyads
|domain error
   3 (<@[ , <@]) 'a'   NB. Execute as monads on the appropriate argument
+-+-+
|3|a|
+-+-+

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Related Primitives

Left (x [ y)

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Use These Combinations

Combinations using x ] y that have exceptionally good performance include:

What it does	Type; Precisions; Ranks	Syntax	Variants; Restrictions	Benefits; Bug Warnings
Fetch from multiple index lists (each row of x is one index list into y)		x (<"1@[ { ]) y		avoids boxing x
Monadic power whose power depends on x		x f@]^:g y (f is any verb)		Applies f rather than x&(f@]) (very small improvement)

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