Regroup the contiguous elements of a vector under a single value. Which elements should
be regrouped is indicated by the rows of a matrix. Output vector is NOT a factor.
Column vector which values are going to be replaced
regroupMatrix
Bounds of the values to regroup under the same modality
modalities
Specify the values of the modalities to use. Must match number of rows
of regroupMatrix
If not specified, replacement modalities will be 1:length(column)