Conversion of Several Variables to Factors

December 15, 2011
By

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..often needed when preparing data for analysis (and usually forgotten until I need it for the next time).
With the below code I convert a set of variables to factors – it could be that there are slicker ways to do it (if you know one let me know!)

> dat <- data.frame(matrix(sample(1:40), 4, 10, dimnames = list(1:4, LETTERS[1:10])))
> str(dat)
'data.frame': 4 obs. of 10 variables:
$ A: int 5 34 3 15
$ B: int 28 25 17 24
$ C: int 2 12 10 32
$ D: int 16 27 29 14
$ E: int 40 7 4 31
$ F: int 22 30 6 18
$ G: int 33 36 35 38
$ H: int 19 21 37 8
$ I: int 20 11 9 26
$ J: int 39 13 1 23
>
> id <- which(names(dat)%in%c("A", "F", "I"))
> dat[, id] <- lapply(dat[, id], as.factor)
> str(dat[, id])
'data.frame': 4 obs. of 3 variables:
$ A: Factor w/ 4 levels "3","5","15","34": 2 4 1 3
$ F: Factor w/ 4 levels "6","18","22",..: 3 4 1 2
$ I: Factor w/ 4 levels "9","11","20",..: 3 2 1 4

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