`accumarray`

Groups values by index and sums each group.

Category: Data Import and Analysis > Preprocessing Data

Syntax

A = accumarray(subs, vals)

Adds up the elements of vals that share the same value in subs.

Description

accumarray is a compact way to compute group totals, a histogram with weights, or a count per category. Think of subs as group labels and vals as the data: the output at position k collects everything labeled k.

Using a scalar for vals counts how many times each index occurs (with vals = 1).

Input arguments

subs: Column vector of positive integer indices; each says which output element receives the matching value.
vals: Column vector of values, one per index, or a scalar that is added once per index.

Output arguments

A: Column vector whose length is max(subs); element k is the sum of the values whose index is k. Positions that never appear hold 0.

Example

Totals per group

subs = [1; 2; 1; 3];
vals = [10; 20; 30; 40];
accumarray(subs, vals)
accumarray([2; 3; 3; 3], 1)

Output

accumarray