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applyPairs -- apply a function to each pair in a hash table

Usage:

applyPairs(H, f)
Inputs:
- H, a hash table, a basic list, or a dictionary, or any instance of a class with an iterator method installed
- f, a function, of two arguments, returning a pair or null
Outputs:
- a hash table, obtained by applying f to each key/value pair in H

Description

i1 : H = new HashTable from {1 => 10, 2 => 15, 3 => 20}

o1 = HashTable{1 => 10}
               2 => 15
               3 => 20

o1 : HashTable

i2 : applyPairs(H, (k,v) -> (k+1, v+10))

o2 = HashTable{2 => 20}
               3 => 25
               4 => 30

o2 : HashTable

i3 : applyPairs(H, (k,v) -> (v,k))

o3 = HashTable{10 => 1}
               15 => 2
               20 => 3

o3 : HashTable

If H is not a hash table, then apply(pairs H, f) is called.

i4 : applyPairs({4, 5, 6}, (i, x) -> i * x)

o4 = {0, 5, 12}

o4 : List

Caveat

It is an error for the function f to return two pairs with the same key.

See also

hash tables
applyKeys -- apply a function to each key in a hash table
applyValues -- apply a function to each value in a hash table
pairs -- list the pairs in a hash table, dictionary, or basic list
scanPairs -- apply a function to the pairs in a hash table

Ways to use applyPairs:

applyPairs(BasicList,Function)
applyPairs(Dictionary,Function)
applyPairs(HashTable,Function)
applyPairs(Thing,Function)

For the programmer

The object applyPairs is a compiled function.

The source of this document is in Macaulay2Doc/functions/applyPairs-doc.m2:43:0.