Why does the sequence operator 0-2:-4 lead to -2 -1 0 1 2 3 4?

Question

Typing in 0-2:-4 returns [1] -2 -1 0 1 2 3 4 in the console. Can anyone explain the logic behind this?

It's in the R-FAQ (sort of): See section 7.33 and ?Syntax. Your expression is being interpreted as 0 minus seq( 2, -4). The unary "-"-operator has higher precedence than the "colon" and the colon ":"-operator has higher precedence than a binary minus. — IRTFM, Feb 01 '17 at 18:34
Just a general note - if you something isn't doing what you expect and you post here it wouldn't hurt to tell us what you expect. I see your code and know how R deals with these things so in my mind it looks exactly like it should. This is a simple example and it's easy enough to figure out what you probably intended it to do but if you're asking a question it is a good idea to clarify what your expectations were. — Dason, Feb 01 '17 at 18:47

score 7 · Answer 1 · edited Feb 01 '17 at 18:32

7

Because of the order of operation:

0 - (2:-4)

which expands to

0 - c(2, 1, 0, -1, -2, -3, -4)

See ?Syntax for more details, including a complete list of binary operators in order of precedence.

edited Feb 01 '17 at 18:32

Gregor Thomas

answered Feb 01 '17 at 18:29

r2evans

Good edit, thanks @Gregor. (Don't think I've actually read that page yet ... :-) – r2evans Feb 01 '17 at 18:33

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