Implementation

A simple benchmark is done by saving proc.time() before running code and subtract the value from new proc.time() after code runs.

t <- proc.time()['elapsed']
invisible(runif(100))
proc.time()['elapsed'] - t

## elapsed 
##   0.006

However, hooks are functions, and bodies of functions are evaluated in different environments every time.

f <- function() environment()
c(f(), f())

## [[1]]
## <environment: 0x563a7b3ceb08>
## 
## [[2]]
## <environment: 0x563a7b3ce910>

Thus, an implementing hook function has to know environment to save proc.time(), and to call the saved proc.time().

Fortunately, the hook with envir argument enables it because envir captures an environment in which a code chunk is evaluated.

In addition, the hook needs to know if they are called before or after a code chunk, which is possible by using before argument.

Finally, the hook is implemented as below.

library(knitr)
knit_hooks$set(
  time = function(before, envir) {
    t <- proc.time()['elapsed']
    if(before) {
      envir$.elapsed <- t
    } else {
      paste(signif(t - envir$.elapsed), 'sec.')
    }
  }
)

Use this hook by setting time = TRUE as a chunk option.

FYI, returning value must be a character to be printed, and signif() is used to focus on significant digits.

Test

```{r, time = TRUE}
head(x)
```

##   Sepal.Length Sepal.Width Petal.Length Petal.Width Species
## 1          5.1         3.5          1.4         0.2  setosa
## 2          4.9         3.0          1.4         0.2  setosa
## 3          4.7         3.2          1.3         0.2  setosa
## 4          4.6         3.1          1.5         0.2  setosa
## 5          5.0         3.6          1.4         0.2  setosa
## 6          5.4         3.9          1.7         0.4  setosa

0.041 sec.

Great!

Question

Is there any way to see benchmark result right after evaluating chunks in RStudio’s editor? I see the results after knitting.

Tip

If you are using R Notebook, just preview it and you can see benchmark results.