Convert a character vector of mixed numbers, fractions, and integers to numeric

Question

I'm trying to write an R function to convert fractions and mixed numbers to decimals. e.g.

mixedToFloat <- function(x){
    x <- sub(' ', '+', x, fixed=TRUE)
    return(unlist(lapply(x, function(x) eval(parse(text=x)))))
}

> mixedToFloat(c('1 1/2', '2 3/4', '2/3', '11 1/4', '1'))
[1]  1.5000000  2.7500000  0.6666667 11.2500000  1.0000000

This works for most of the cases I can think of, but feels a little bit hackish. Is there a more standard way to do this?

Answer 1

1) This uses strapplyc to extract the numbers and then calc puts them in standard form, converts them to numeric and performs the calculation:

library(gsubfn)

ff <- c('1 1/2', '2 3/4', '2/3', '11 1/4', '1')
calc <- function(s) {
    x <- c(if (length(s) == 2) 0, as.numeric(s), 0:1)
    x[1] + x[2] / x[3]
}
sapply(strapplyc(ff, "\\d+"), calc)

2) A different approach is to convert each expression into valid R code and then parse and evaluate each.

sapply(sub(" ", "+", ff), function(x) eval(parse(text = x)))
##      1 1/2      2 3/4        2/3     11 1/4          1 
##  1.5000000  2.7500000  0.6666667 11.2500000  1.0000000 

Answer 2

Anything less "hackish" will have to parse your inputs and match them to a number of pre-defined patterns. I came up with this:

mixedToFloat <- function(x){
  is.integer  <- grepl("^\\d+$", x)
  is.fraction <- grepl("^\\d+\\/\\d+$", x)
  is.mixed    <- grepl("^\\d+ \\d+\\/\\d+$", x)
  stopifnot(all(is.integer | is.fraction | is.mixed))

  numbers <- strsplit(x, "[ /]")

  ifelse(is.integer,  as.numeric(sapply(numbers, `[`, 1)),
  ifelse(is.fraction, as.numeric(sapply(numbers, `[`, 1)) /
                      as.numeric(sapply(numbers, `[`, 2)),
                      as.numeric(sapply(numbers, `[`, 1)) +
                      as.numeric(sapply(numbers, `[`, 2)) /
                      as.numeric(sapply(numbers, `[`, 3))))
}

mixedToFloat(c('1 1/2', '2 3/4', '2/3', '11 1/4', '1'))
# [1]  1.5000000  2.7500000  0.6666667 11.2500000  1.0000000