agenis agenis - 1 year ago 67
R Question

Getting system.time work with piping %>%

I tend to use the piping operator a lot (

, from
, or
library). Until one day I tried to use the
command on the left hand-side.

system.time(mean(rnorm(1E7))) # ok
#### user system elapsed
#### 3.52 0.05 3.58
rnorm(1E7) %>% mean %>% system.time # ?
#### user system elapsed
#### 0 0 0

So I went reading the documentation and I tried this (it says you can force the evaluation of RHS first by enclosing it in parenthesis, but it gives the same behaviour.

rnorm(1E7) %>% mean %>% (function(x) system.time(x))
#### user system elapsed
#### 0 0 0

My question is the following:

1. Why exactly is the command
not working as expected when placed at the end of a piping line?

2. Is there a way to measure the calculation time of a line of code composed of pipings, without having to place the whole line inside parenthesis (which would annihilate the practical benefits of piping...) or using proc.time?

Answer Source

Second best I can do is to make a wrapper on system.time that takes an unevaluated expression and evaluates it, and then you have to wrap the timed expression in curly brackets and quote it when you pipe it so it isn't evaluated until my wrapper function gets its paws on it:

> psystime = function(e){system.time(eval(e))}
> quote({rnorm(1e7) %>%  mean}) %>% psystime
   user  system elapsed 
  0.764   0.004   0.767 

I say second best, because the best answer is simply not to do this at all. Sometimes pipes are the problem, not the solution.

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