[Rd] Unexpected behavior of '[' in an apply instruction
Rui Barradas
ru|pb@rr@d@@ @end|ng |rom @@po@pt
Fri Feb 12 12:25:48 CET 2021
Hello,
This came up in this StackOverflow post [1].
If x is an array with n dimensions, how to subset by just one dimension?
If n is known, it's simple, add the required number of commas in their
proper places.
But what if the user doesn't know the value of n?
The example below has n = 3, and subsets by the 1st dim. The apply loop
solves the problem as expected but note that the index i has length(i) > 1.
x <- array(1:60, dim = c(10, 2, 3))
d <- 1L
i <- 1:5
apply(x, MARGIN = -d, '[', i)
x[i, , ]
If length(i) == 1, argument drop = FALSE doesn't work as I expected it
to work, only the other way does:
i <- 1L
apply(x, MARGIN = -d, '[', i, drop = FALSE)
x[i, , drop = FALSE]
What am I missing?
[1]
https://stackoverflow.com/questions/66168564/is-there-a-native-r-syntax-to-extract-rows-of-an-array
Thanks in advance,
Rui Barradas
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