reduce

Collapse a list to a single value by repeated pairwise combination.

Synopsis

my $result = reduce { BLOCK } @list;
my $sum    = reduce { $a + $b } 1..10;       # 55
my $max    = reduce { $a > $b ? $a : $b } @xs;

The block is called in scalar context with $a set to the running accumulator and $b set to the next element. On the first call, $a and $b are the first two elements; on each subsequent call, $a is whatever the previous call returned.

What you get back

The value of the last block invocation. If the list is empty, undef is returned. If the list contains exactly one element, that element is returned and the block is not called.

Examples

my $concat = reduce { "$a,$b" } 'a'..'c';    # 'a,b,c'
my $best   = reduce { $a->score > $b->score ? $a : $b } @players;
my $total  = reduce { $a + length $b } 0, @strings;   # sum of lengths

## Guarantee a numeric identity so an empty @values doesn't yield undef:

my $sum = reduce { $a + $b } 0, @values;

Differences from upstream

Fully compatible with upstream.

See also

• reductions — like reduce, but also keeps the intermediate values.

• sum / product / min / max — specialised, faster forms.

• first / any / all — element-test reductions over $_.