Finding a last digits

[kmmukesh]

Dear all,
I just wanted to know if there is a way to find out last digit or first digit in a numeric values using R? like the one we have with LEFT, RIGHT functions in excel?

thank you for your reply!

BR, M

[siddharthprabhu]

Hi @kmmukesh, welcome to RStudio Community.

The stringr package has functions that can help you accomplish this. Here's an illustration using the built-in mtcars data set.

library(stringr)

mtcars$disp
#>  [1] 160.0 160.0 108.0 258.0 360.0 225.0 360.0 146.7 140.8 167.6 167.6 275.8
#> [13] 275.8 275.8 472.0 460.0 440.0  78.7  75.7  71.1 120.1 318.0 304.0 350.0
#> [25] 400.0  79.0 120.3  95.1 351.0 145.0 301.0 121.0

# Get first digit of the disp variable for each car.
str_extract(mtcars$disp, "^\\d")
#>  [1] "1" "1" "1" "2" "3" "2" "3" "1" "1" "1" "1" "2" "2" "2" "4" "4" "4" "7" "7"
#> [20] "7" "1" "3" "3" "3" "4" "7" "1" "9" "3" "1" "3" "1"

# Get last integer digit of the disp variable for each car.
str_extract(mtcars$disp, "\\d$")
#>  [1] "0" "0" "8" "8" "0" "5" "0" "7" "8" "6" "6" "8" "8" "8" "2" "0" "0" "7" "7"
#> [20] "1" "1" "8" "4" "0" "0" "9" "3" "1" "1" "5" "1" "1"

# Get last decimal digit of the disp variable for each car.
str_match(mtcars$disp, "\\.(\\d$)")[, 2]
#>  [1] NA  NA  NA  NA  NA  NA  NA  "7" "8" "6" "6" "8" "8" "8" NA  NA  NA  "7" "7"
#> [20] "1" "1" NA  NA  NA  NA  NA  "3" "1" NA  NA  NA  NA


# An alternate approach that is similar to Excel's LEFT and RIGHT functions.

# Get first digit of the disp variable for each car.
str_sub(mtcars$disp, start = 1L, end = 1L)
#>  [1] "1" "1" "1" "2" "3" "2" "3" "1" "1" "1" "1" "2" "2" "2" "4" "4" "4" "7" "7"
#> [20] "7" "1" "3" "3" "3" "4" "7" "1" "9" "3" "1" "3" "1"

# Get last integer digit of the disp variable for each car (only works correctly
# if each number is of the same length).
str_sub(mtcars$disp, start = 3L, end = 3L)
#>  [1] "0" "0" "8" "8" "0" "5" "0" "6" "0" "7" "7" "5" "5" "5" "2" "0" "0" "." "."
#> [20] "." "0" "8" "4" "0" "0" ""  "0" "." "1" "5" "1" "1"

# Get last decimal digit of the disp variable for each car (only works correctly
# if each number is of the same length).
str_sub(mtcars$disp, start = 5L, end = 5L)
#>  [1] ""  ""  ""  ""  ""  ""  ""  "7" "8" "6" "6" "8" "8" "8" ""  ""  ""  ""  "" 
#> [20] ""  "1" ""  ""  ""  ""  ""  "3" ""  ""  ""  ""  ""

^{Created on 2020-03-23 by the reprex package (v0.3.0)}

[kmmukesh]

Thanks, Sid. It helps!

[siddharthprabhu]

Great! If I solved your query, would you mind marking my post as a solution?

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[kmmukesh]

Sure, I will. Can I ask you one more leading question-
I have decimal values like 103.5, 36.8, 125.8- When I used a str_extract function, I am getting the last digit like "5", "8", "8". Is there a workaround to find to find out the decimal point as well like "0.5", "0.8", "0.8"
Thanks,
M

[siddharthprabhu]

EDIT: I've updated my original post with an alternate way of doing this which is similar to how you would use the LEFT and RIGHT functions in Excel. Added a solution for finding the last decimal digit as well.