DATA MINING
Desktop Survival Guide by Graham Williams |
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Apply |
Suppose you have a data frame from which you wish to extract a subset of rows, and you have a matrix to record the start and finish of the sequences of indicies you wish to extract. Whilst a for loop is obvious, mapply works nicely.
> x <- rbind(c(2,5), c(7,9), c(15,20)) > x [,1] [,2] [1,] 2 5 [2,] 7 9 [3,] 15 20 > unlist(mapply(seq, x[,1], x[,2])) [1] 2 3 4 5 7 8 9 15 16 17 18 19 20 |