# Is there something method in ruby like python's reduce()?

**URL:** <https://www.ruby-forum.com/t/is-there-something-method-in-ruby-like-pythons-reduce/87094>\
**Category:** Ruby\
**Created:** [February 28, 2007, 3:13am UTC](https://www.ruby-forum.com/t/is-there-something-method-in-ruby-like-pythons-reduce/87094 "2007-02-28T03:13:06Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![lnes](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/c0e974/32.png) [@lnes](https://www.ruby-forum.com/u/lnes)\
**Post date:** [February 28, 2007, 3:13am UTC](https://www.ruby-forum.com/t/is-there-something-method-in-ruby-like-pythons-reduce/87094/1 "2007-02-28T03:13:06Z")

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there is python’s build-in function reduce()'s definition

# ===================================================================== reduce( function, sequence[, initializer]) Apply function of two arguments cumulatively to the items of sequence, from left to right, so as to reduce the sequence to a single value. For example, reduce(lambda x, y: x+y, [1, 2, 3, 4, 5]) calculates ((((1+2)+3)+4)+5). The left argument, x, is the accumulated value and the right argument, y, is the update value from the sequence. If the optional initializer is present, it is placed before the items of the sequence in the calculation, and serves as a default when the sequence is empty. If initializer is not given and sequence contains only one item, the first item is returned.

thanks.

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**Author:** ![lnes](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/c0e974/32.png) [@lnes](https://www.ruby-forum.com/u/lnes)\
**Post date:** [February 28, 2007, 3:19am UTC](https://www.ruby-forum.com/t/is-there-something-method-in-ruby-like-pythons-reduce/87094/2 "2007-02-28T03:19:07Z")

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On 2/27/07, lnes [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> # optional initializer is present, it is placed before the items of the sequence in the calculation, and serves as a default when the sequence is empty. If initializer is not given and sequence contains only one item, the first item is returned.

ri Enumerable#inject

thanks.

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<div class="post-metadata">

**Author:** ![lnes](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/c0e974/32.png) [@lnes](https://www.ruby-forum.com/u/lnes)\
**Post date:** [February 28, 2007, 5:18am UTC](https://www.ruby-forum.com/t/is-there-something-method-in-ruby-like-pythons-reduce/87094/3 "2007-02-28T05:18:37Z")

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it’s very useful, thanks!

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<div class="post-metadata">

**Author:** ![lnes](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/c0e974/32.png) [@lnes](https://www.ruby-forum.com/u/lnes)\
**Post date:** [February 28, 2007, 3:22am UTC](https://www.ruby-forum.com/t/is-there-something-method-in-ruby-like-pythons-reduce/87094/4 "2007-02-28T03:22:07Z")

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On 2/27/07, lnes [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> there is python’s build-in function reduce()'s definition

There’s Enumerable#inject:

enum.inject(initial) {| memo, obj | block } =\> obj  
enum.inject {| memo, obj | block } =\> obj

Combines the elements of enum by applying the block to an accumulator  
value (memo) and each element in turn. At each step, memo is set to  
the value returned by the block. The first form lets you supply an  
initial value for memo. The second form uses the first element of the  
collection as a the initial value (and skips that element while  
iterating).

# Sum some numbers

(5…10).inject {|sum, n| sum + n } #=\> 45

# Multiply some numbers

(5…10).inject(1) {|product, n| product \* n } #=\> 151200

# find the longest word

longest = %w{ cat sheep bear }.inject do |memo,word|  
memo.length \> word.length ? memo : word  
end  
longest #=\> “sheep”

# find the length of the longest word

longest = %w{ cat sheep bear }.inject(0) do |memo,word|  
memo \>= word.length ? memo : word.length  
end  
longest #=\> 5

It works for Arrays and any other classes that include the Enumerable  
module.