Reduce
Reduce
First: What is 'reduce'?
In very short, reduce applies the function of two arguments cumulatively to the items of iterable, from left to right, so as to reduce the iterable to a single value.
The left argument is the accumulated value and the right argument is the update value from the iterable.
The Syntax
reduce(function, iterable)
- The function can be a function or a lambda expression.
-
This function must work on 2 arguments. One is the result of the previous run of the function (the accumulated value). The other is the next item in the iterable.
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The iterable can be any iterable - list, string, etc.
A few examples:
These examples are for demonstration of reduce. There are simpler ways to accomplish the same thing that these examples do.
For all these examples, we'll use this iterable: list = [47, 11, 42, 102, 13]
1. reduce((lambda a, b: a if a > b else b), list)
This returns the greatest of all numbers in the list.
The a is the result of the a > b. And b is the next item in the list. If a is greater than b, then the value in a remains in a, else the value of b becomes the a. See below in this chart.
| round # | a | b | a>b * |
|---|---|---|---|
and the final a is 102
2. reduce((lambda a,b: a + b), list)
This returns the sum of all numbers in the list.
The a is the result of the a + b. And b is the next item in the list.
| round # | a | b | a + b |
|---|---|---|---|
and the final a is 215
3. reduce(lambda a, b: str(a)+str(b), list)
This returns the concatenation of all numbers in the list.
The a is the result of the str(a)+str(b). And b is the next item in the list.
| round # | a | b | str(a)+str(b) |
|---|---|---|---|
and the final a is '47114210213'
--- so this can be used to concatenate items in a list