extract first digit of one column into other column!

[emri]

Hello everyone,

I've come upon something I'm a bit unsure about:

Basically, I have a dataset where one column is a series of three digit codes. I only really need the first digit of those codes though for my analysis. For this reason, I want to create a new column containing only the first digit of that column, so I can do some dummy variables based on that. For example, if A is the original column, I want to create column B, as below:

A B
123 1
999 9
222 2

Anyone got an idea how to do this? I can't find anything online. Alternatively, if its possible to base dummy variables based on only the first digit of A, without creating B, that would also work.

Thanks!

[pieterjanvc]

Hi there,

This can easily be done using a simple bit of RegEx

myData = data.frame(A = c("123", "999", "222"))
myData$B = stringr::str_extract(myData$A, "\\d")

The expression "\d" means that to take the first digit (\d). Since the expression is written as a string, you need to escape the "\" hence "\\"

If you like to learn more of regular expressions, here is a great online site to get started:
https://regexone.com/

Hope this helps,
PJ

[andresrcs]

I think RegEx might be an overkill for this simple task, you can get away with using base R substr()

sample_df <- data.frame(A = c("123", "999", "222"))
sample_df$B <- substr(sample_df$A, 1, 1)
sample_df
#>     A B
#> 1 123 1
#> 2 999 9
#> 3 222 2

^{Created on 2022-02-06 by the reprex package (v2.0.1)}