Digit sum function in R

Question

I was looking for the quite basic numeric function digit sum in R.

• I did not find a preinstalled function.
• Even in Stackoverflow\'s extensive R libra

Answer 1

I wondered which of the three suggested methods (plus a fourth one) is the fastest so I did some benchmarking.

1. digitsum1 <- function(x) sum(as.numeric(unlist(strsplit(as.character(x), split = ""))))

2. digitsum2 <- function(x) sum(floor(x / 10^(0:(nchar(x) - 1))) %% 10)

3. Using function digitsBase from package GLDEX:

   library(GLDEX, quietly = TRUE)
   digitsum3 <-  function(x) sum(digitsBase(x, base = 10))
   

4. Based on a function by Greg Snow in the R-help mailing list:

   digitsum4 <- function(x) sum(x %/% 10^seq(0, length.out = nchar(x)) %% 10)

Benchmark code:

library(microbenchmark, quietly = TRUE)
# define check function
my_check <- function(values) {
  all(sapply(values[-1], function(x) identical(values[[1]], x)))
}
x <- 1001L:2000L
microbenchmark(
  sapply(x, digitsum1),
  sapply(x, digitsum2),
  sapply(x, digitsum3),
  sapply(x, digitsum4),
  times = 100L, check = my_check
)

Benchmarks results:

#> Unit: milliseconds
#>                  expr   min    lq  mean median    uq   max neval
#>  sapply(x, digitsum1)  3.41  3.59  3.86   3.68  3.89  5.49   100
#>  sapply(x, digitsum2)  3.00  3.19  3.41   3.25  3.34  4.83   100
#>  sapply(x, digitsum3) 15.07 15.85 16.59  16.22 17.09 24.89   100
#>  sapply(x, digitsum4)  9.76 10.29 11.18  10.56 11.48 45.20   100

Variant 2 is slightly faster than variant 1 while variants 4 and 3 are much slower. Although the code of variant 4 seems to be similar to variant 2, variant 4 is less efficient (but still better than variant 3).

Full benchmark results (including graphs) are on github.

Answer 2

I'm not sure why you would think there would be an inbuilt function to do that. It not really a statistical operation. More of a number theory sort of procedure. (There are many examples that can be found with a search of the Rhelp Archives. I use Markmail for that purpose but there are other search engines like RSeek, GMane, and the Newcastle webpage. Your function would take a series of numbers and return a single number that was the digit sum of all of them. If that were the goal then it looks reasonably designed. I would have guessed that one would want the digit sums from each number:

sapply( c(1,2,123), 
        function(x) sum( as.numeric(unlist(strsplit(as.character(x), split=""))) ))
[1] 1 2 6

There is a "digitizing" funciton digitsBase in pkg:GLDEX, and you could replace your as.numeric(unlist(split(as.character(x),""))) with that function:

digitsBase(x, 10)

Answer 3

This should be better:

digitsum <- function(x) sum(floor(x / 10^(0:(nchar(x) - 1))) %% 10)

Answer 4

What I do for finding the sum of digits in R :

x = readline("Enter the number")
a = as.integer(c(strsplit(x,split="")[[1]]))
print((sum(a)))