“[” with the apply() functions, revisited

April 29, 2014
By

(This article was first published on The stupidest thing... » R, and kindly contributed to R-bloggers)

I’d mentioned in the fall that one could use "[" in the apply-type functions, like this:

id <- c("ZYY-43S-CWA3", "6YU-F4B-VD2I")
sapply(strsplit(id, "-"), "[", 2)

I just realized that you can use this with matrices, too. If you have a list of matrices, you can pull out rows and columns with this technique.

z <- list(matrix(1:10, nrow=2), matrix(11:20, nrow=2))
lapply(z, "[", 1, )
lapply(z, "[", , 3)

As you can see, my data isn’t “tidy.”

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