> How is it possible to group rows of a matrix or a data frame by the same
> values
> of the first column?
If you mean _group_ as in SQL GROUP BY, use aggregate() with a count or summary
statistic.
If you mean _sort_, just to get similar values close together, use order()
For example, to sort by the first column of a matrix mm:
oo <- order(mm[,1])
mm[oo,]
order() also takes multiple sort fields so can sort by several columns
simultaneously (eg sort by first column and within that by third column etc).
S Ellison
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