Test if string have a specific number in a specific position in R-CodePudding

I have a dataframe with a variable containing number of 9 digits. I would like to create a new variable with mutate and ifelse that will depend on the value of the 7th digit. I saw the grepl function that could do what I want but I don't know how to write this code.

For example if the 7th digit is a 1, I would like to have 1 in the new variable, if the 7th digit is a 2, I would like a 5 in the new variable, and if the 7th digit is a 3, I would like a 6 in the new variable.

Please find a example of data below.

Thank you for your help

# Library
library(tidyverse)

# Data 
ID=c(1,2,3,4,5,6)
Vectest2=c("9079870989", "907007123", "907865345", "907098432", "907347567", "907845120")


> data
  ID   Vectest
1  1 830008100
2  2 830056123
3  3 830678309
4  4 830008100
5  5 830056123
6  6 830678309

data=data.frame(ID, Vectest)

# code 

data %>% mutate(variable2=ifelse( grepl(), 3, 
                          ifelse( grepl(), 1,
                          ifelse( grepl(), 2, NA)))

CodePudding user response：

Instead of grepl I would suggest to you substr since you have to check fixed position. I have created a new column called seventh_d which will save the 7th digit in a variable so you don't have to calculate it again and again.

Also, since you are using dplyr use case_when which is a better alternative of nested ifelse.

library(dplyr)

data %>% 
  mutate(seventh_d = substr(Vectest2, 7, 7), 
         variable2 = case_when(seventh_d == 1 ~ 1, 
                               seventh_d == 2 ~ 5,
                               seventh_d == 3 ~ 6, 
                               TRUE ~ NA_real_))

#  ID   Vectest2 seventh_d variable2
#1  1 9079870989         0        NA
#2  2  907007123         1         1
#3  3  907865345         3         6
#4  4  907098432         4        NA
#5  5  907347567         5        NA
#6  6  907845120         1         1

data

data = data.frame(ID, Vectest2)