What does '[' (left square bracket) do when treated as a function?

Asked Mar 25 '19 at 15:27

Active Mar 25 '19 at 17:55

Viewed 44 times

I tried a simple test, but I am not sure how to interpret the results correctly.

a <- 1:10
b <- lapply(a,'[',2)

The code I am analyzing used the lapply function along with the arguments listed above.

The output confused me as it gave me a list of 10 int values, all of which were NA. This probably means a needs to be a list, but I am not sure.

I couldn't find anything with a google search, and I am not sure how to interpret my test (if I even used it in the correct context).

edited Mar 25 '19 at 17:55

d.b

asked Mar 25 '19 at 15:27

hkj447

5

That'd be similar to `b = lapply(a, function(x) x[2])` – d.b Mar 25 '19 at 15:30
4

...which is why it returns all NAs; it treats each element of `a` as a length one vector and tries to extract the 2nd element, which doesn't exist. – joran Mar 25 '19 at 15:31
Look at `help(Extract)`. – NelsonGon Mar 25 '19 at 15:46
Try, `my_list = list(1:5, 2:6, 3:7)` as your input. – Gregor Thomas Mar 25 '19 at 18:16

0 Answers0