Select every other element from a vector

Question

Let\'s say I had a vector:

remove <- c(17, 18, 19, 20, 24, 25, 30, 31, 44, 45).

How do I select / extract every second value in the vector? L

Answer 1

remove[seq(1,length(remove),2)]

Answer 2

Just another alternative:

> remove[seq_along(remove) %% 2 > 0]
[1] 17 19 24 30 44

Answer 3

remove[c(TRUE, FALSE)]

will do the trick.

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How it works?

If logical vectors are used for indexing in R, their values are recycled if the index vector is shorter than the vector containing the values.

Here, the vector remove contains ten values. If the index vector c(TRUE, FALSE) is used, the actual command is: remove[c(TRUE, FALSE, TRUE, FALSE, TRUE, FALSE, TRUE, FALSE, TRUE, FALSE)]

Hence, all values with odd index numbers are selected.