How R handles repeated arithmetic signs

Agnes5 days ago

I mistakenly put an extra + into my R code and found that it raised no complaint whatsoever.

Actually, after trying a few more things, I found R behaves rather strangely if several operators appear together.

Could somebody explain the reason, and which operations get evaluated first?


6 + 2
#> [1] 8

6 +++ 2
#> [1] 8

6 --- 2
#> [1] 4

6 +-+ 2
#> [1] 4

6 -+- 2
#> [1] 8

The conversation continues 2

Follow the reasoning

mulchpile5 days ago Permalink
```
lobstr::ast(6 +++ 2)
#█─`+` 
#├─6 
#└─█─`+` 
#  └─█─`+` 
#    └─2
```
Every operator after the initial one is treated as unary, meaning the function-call equivalent is +(6, +(+(2))).
liv_n5 days ago Permalink
R allows +/- to serve as unary or binary operators, with unary taking precedence. so the initial sign is the actual binary operation, while the remaining signs form nested unary +/- operations on the right-hand number. unary + leaves it unchanged, unary - reverses its sign each time.

so 6 +++ 2 amounts to 6 + (+(+2)) = 8, while 6 --- 2 becomes 6 - (-(-2)) = 4. the remaining two sequences work similarly, count the minus signs after the first operator (even means positive, odd means negative).