[x] u&v y Compose Conjunction
Applies v to each cell of each argument, and then applies u to the result(s) of v for each cell separately
('Ike';'James') >&#&> ('Newton';'Bond') NB. Is first name longer than last name? 0 1
This contrasts with u&:v which applies v to the entire argument(s) and then applies u on the entire result(s) of v .
- Operand v is executed monadically.
- Operand u is executed either monadically or dyadically depending whether u&v has been called monadically or dyadically.
The monadic use of & is deprecated. Use @ instead. Some compounds of the form f&g are not recognized for special code in places where f@g is recognized, if only the monadic form of the compounds is eligible for special treatment.
*:&+: 3 4 5 NB. double, then square. Applied to each atom 36 64 100 *: +: 3 4 5 NB. Same result if applied to entire list 36 64 100 +/&+: 3 4 5 NB. Double, then "total". Applied to each atom. 6 8 10 +/ +: 3 4 5 NB. Not the same if applied to entire list! 24
]firstname =: 'Dennis';'Richard';'Ken' +------+-------+---+ |Dennis|Richard|Ken| +------+-------+---+ ]lastname =: 'Ritchie';'Stallman';'Iverson' +-------+--------+-------+ |Ritchie|Stallman|Iverson| +-------+--------+-------+ firstname ,&> lastname NB. Join each first name to last, individually DennisRitchie RichardStallman KenIverson (>firstname) , (>lastname) NB. very different applied to entire array Dennis Richard Ken Ritchie Stallman Iverson firstname (>@[ , >@])"0 lastname NB. equivalent form DennisRitchie RichardStallman KenIverson
1. ([x] u&v y) is the same as ([x] u&:v"mv y) (where mv is the monadic rank of v).
The second phrase uses Appose (&:) instead of Compose (&).
2. The difference between Appose (u&:v) and Compose (u&v) is shown in the last two columns of the diagram below:
3. So what's the difference between Atop (@) and Compose (&) ?
None at all, for the monads (u@v) and (u&v)
u&v y ↔ u v y u@v y ↔ u v y
But the dyads are different
x u&v y ↔ (v x) u (v y) x u@v y ↔ u x v y
According to the J Dictionary -- &: is equivalent to & except that the ranks of the resulting function are infinite; the relation is similar to that between @: and @
1. The J Dictionary states that u&v y <==> u v y and x u&v y <==> (v x) u (v y), but these statements assume that u&v is applied at the rank mv as defined above.
The correct equivalences for u&v are given above.
2. Note also that in u&f&v, f will be applied monadically. If the whole expression is called dyadically, then v is applied to each argument, f applied monadically to each result of v, and then u applied dyadically to the results. Equivalent to fork (f@v@[ u f@v@]).