selectPairs -- select a part of a hash table by pairs

Usage:

selectPairs(x, f)

selectPairs(n, x, f)
Inputs:
- n, an integer,
- x, a hash table or a basic list,
- f, a function,
Outputs:
- a hash table or a basic list, containing all (or n, if it is given) key-value pairs (k,v) from x for which f(k,v) evaluates to true.

Description

i1 : x = hashTable{(1, 2), (2, 4), (3, 6), (4, 8), (5, 10)}

o1 = HashTable{1 => 2 }
               2 => 4
               3 => 6
               4 => 8
               5 => 10

o1 : HashTable

i2 : selectPairs(x, (k,v) -> odd(k + v))

o2 = HashTable{1 => 2 }
               3 => 6
               5 => 10

o2 : HashTable

i3 : selectPairs(2, x, (k, v) -> odd(k + v))

o3 = HashTable{1 => 2}
               3 => 6

o3 : HashTable

If x is not a hash table, then select(pairs x, f) (or select(n, pairs x, f)) is called.

i4 : selectPairs(toList(1..10), (i, x) -> even x)

o4 = {(1, 2), (3, 4), (5, 6), (7, 8), (9, 10)}

o4 : List

i5 : selectPairs(3, toList(1..10), (i, x) -> even x)

o5 = {(1, 2), (3, 4), (5, 6)}

o5 : List

Caveat

If x is a hash table, then it must be immutable.

Ways to use selectPairs:

selectPairs(BasicList,Function)
selectPairs(HashTable,Function)
selectPairs(ZZ,BasicList,Function)
selectPairs(ZZ,HashTable,Function)

For the programmer

The object selectPairs is a compiled function.

The source of this document is in Macaulay2Doc/functions/select-doc.m2:295:0.

selectPairs -- select a part of a hash table by pairs

Description

Caveat

See also

Ways to use selectPairs:

For the programmer