Does piping affect operations with sqrt function?-CodePudding

I was doing some calculations and I noticed that when I add pipes it outputs a wrong result. It is the first time I encounter this and I would like to know why it happens to avoid this situation in the future.

# Making the operations separately gives the correct result.
0.58*(1-0.58) # 0.2436
sqrt(0.2436) # 0.4935585

# Adding all calculations in the same line works.
sqrt(0.58*(1-0.58)) # 0.4935585

# Use %>% doesn't give the right result.
0.58*(1-0.58) %>% sqrt() # 0.375883

# The issue doesn't happen when in a df or tibble
tibble(a = c(0.2436)) %>% 
  mutate(b = sqrt(a))
    #  A tibble: 1 × 2
    #      a     b
    #   <dbl> <dbl>
    # 1 0.244 0.494

Thank you,

CodePudding user response：

If you look at ?Syntax, you'll see that subtraction is higher precedence than pipes, and pipes are higher precedence than multiplication.

So in this expression:

0.58 * (1 - 0.58) %>% sqrt()

1 - 0.58 is evaluated to 0.42. Then 0.42 is piped to sqrt(). Then the result is multiplied by 0.58.

sqrt(0.42) * 0.58
[1] 0.375883

You can avoid it by wrapping the left-hand side in parentheses:

(0.58*(1-0.58)) %>% sqrt(.)
[1] 0.4935585

CodePudding user response：

It's happening due to operator precedence. And as always, using parenthesis can save from such unexpected things.

library(magrittr)

(0.58*(1-0.58)) %>% sqrt()
#> [1] 0.4935585


# here multiplication is evaluated after piping.
0.58*(1-0.58) %>% sqrt()
#> [1] 0.375883

# so the above is same as doing this
((1-0.58) %>% sqrt()) * 0.58
#> [1] 0.375883

^{Created on 2022-07-12 by the reprex package (v2.0.1)}