[R] Collapsing/aggregating columns in a matrix

[Barth B. Riley]

Dear list

I want to know if there is a function in R that enables one to create a new matrix based on values in an existing matrix, whereby each column in the new matrix is a row-specific summary (e.g., sum, mean) of multiple columns in the original matrix. For instance, to take a 12-column matrix and collapse it into a 3 column matrix containing the means for each row of columns 1-4, 5-8, and 9-12 of the original matrix. I want to do this with a large number of data matrices where the columns to collapse varies from dataset to dataset.

Thanks

Barth

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