How to sum repeated adjacent values in a vector

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Galgool 2019-4-27

评论： Galgool 2019-4-28

Hi guys,

I have a random vector with -1 and 1.

for example:

X = [1, 1, -1, 1, 1, 1, -1, -1, 1, -1, 1, 1, 1, 1, -1, -1]

I wish to creat a vector that sums repeated adjacent values.

so for the above example:

Y = [2, -1, 3, -2, 1, -1, 4, -2]

any idea?

Cedric 2019-4-27

编辑：Cedric 2019-4-27

Here is one way:

Y = splitapply( @sum, X, [0, cumsum( diff(X) ~= 0 )] + 1 ) ;

or, split into two expressions that make it easier to understand:

groupId = [0, cumsum( diff(X) ~= 0 )] + 1 ;
Y = splitapply( @sum, X, groupId ) ;

Andrei Bobrov 2019-4-27

+1.

accumarray(cumsum(diff([0;X(:)])~=0),X(:));

Galgool 2019-4-28

it does the job. thanks.

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