Bob Bob - 1 year ago 83
R Question

In R, why does using change the result?

For example, if I have a multidimensional list object, say, "x"

x <- list(); x[[1]] <- c(1,2,3); x[[2]] <- c(2,3,4);
x[[3]] <- c(3,4,5); x[[4]] <- c(4,5,6)
a <- combn(x,3)

If I want to combine every row in the first column into a single vector, this doesn't give me what I want:


It returns a list with each element an element of the original list. Instead, this works:,a[1:3,1])

According to the help description, all does is execute a function, so why is the result different?

Answer Source

c(a[1:3,1]) is equivalent here to a[1:3,1] which is equivalent here to a[1:3]. All this does is combine the list, not combine the elements of this list. executes a function call against a list of arguments, in this case, it executes the c function to combine the elements of a.

What you want is c(a[1:3], recursive = TRUE), which descends through the list recursively combining elements into a single vector.

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