How to perform arithmetic on values and operators expressed as strings?

Question

I have a character variable with ratios (proportions) expressed as strings:

x <- c("2/3", "5/6", "3/11").

I want to convert the character values in x into percentages. Thus, my desired output would be:

c(2/3, 5/6, 3/11) * 100
# [1] 66.66667 83.33333 27.27273 

When I try the as.numeric(x), a warning message is generated (NAs introduced by coercion) and all elements are converted into NA

What to do?

Answer 1

Here are some alternatives:

1) read.table Read the text in as if it were a file and then divide:

with(read.table(text = x, sep = "/"), 100 * V1 / V2)
## [1] 66.66667 83.33333 27.27273

2) eval/parse eval/parse is generally frowned upon but here is how it would work:

100 * sapply(as.list(parse(text = x)), eval)
## [1] 66.66667 83.33333 27.27273

3) strsplit

sapply(strsplit(x, "/"), function(x) { x <- as.numeric(x); 100 * x[1] / x[2]})
## [1] 66.66667 83.33333 27.27273

4) gsubfn::strapply This picks out the two strings of digits using strapply and then converts each to numeric and divides:

library(gsubfn)

strapply(x, "(\\d+)/(\\d+)", ~ 100 * as.numeric(x) / as.numeric(y), simplify = TRUE)
## [1] 66.66667 83.33333 27.27273

Answer 2

tidyerse

If you stumbled onto this post in search of a tidyverse answer here is a simple extension. Note this does use the aforementioned "frowned upon" eval( parse())

library(dplyr)
library(purrr)

# add into a tibble
df <- tibble(fractions = c("2/3", "5/6", "3/11"))
df %>% 
  mutate(numbers = map_dbl(fractions, ~eval(parse(text = .x))))
#> # A tibble: 3 x 2
#>   fractions numbers
#>   <chr>       <dbl>
#> 1 2/3         0.667
#> 2 5/6         0.833
#> 3 3/11        0.273