Extracting the last n characters from a string in R

Question

How can I get the last n characters from a string in R  Is there a function like SQL s RIGHT

User · Answer

Another reasonably straightforward way is to use regular expressions and sub:

sub('.*(?=.$)', '', string, perl=T)

So, "get rid of everything followed by one character". To grab more characters off the end, add however many dots in the lookahead assertion:

sub('.*(?=.{2}$)', '', string, perl=T)

where .{2} means .., or "any two characters", so meaning "get rid of everything followed by two characters".

sub('.*(?=.{3}$)', '', string, perl=T)

for three characters, etc. You can set the number of characters to grab with a variable, but you'll have to paste the variable value into the regular expression string:

n = 3
sub(paste('.+(?=.{', n, '})', sep=''), '', string, perl=T)

User · Answer

Try this   x  lt -  some text in a string  n  lt - 5 substr x  nchar x -n  nchar x     It shoudl give    1   string

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Use stri sub function from stringi package  To get substring from the end  use negative numbers  Look below for the examples   stri sub  abcde  1 3   1   abc  stri sub  abcde  1 1   1   a  stri sub  abcde  -3 -1   1   cde    You can install this package from github  https   github com Rexamine stringi  It is available on CRAN now  simply type  install packages  stringi     to install this package

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I used the following code to get the last character of a string        substr output  nchar stringOfInterest   nchar stringOfInterest     You can play with the nchar stringOfInterest  to figure out how to get last few characters

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Just in case if a range of characters need to be picked        For example  to get the date part from the string  substrRightRange  lt - function x  m  n  substr x  nchar x -m 1  nchar x -m n    value  lt -  REGNDATE 20170526RN   substrRightRange value  10  8    1   20170526

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A simple base R solution using the substring   function  who knew this function even existed     RIGHT   function x n     substring x nchar x -n 1      This takes advantage of basically being substr   underneath but has a default end value of 1 000 000   Examples    gt  RIGHT  Hello World   2   1   d    gt  RIGHT  Hello World   8   1   o World

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An alternative to substr is to split the string into a list of single characters and process that    N  lt - 2 sapply strsplit x       function x  n  paste tail x  n   collapse        N

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UPDATE  as noted by mdsumner  the original code is already vectorised because substr is  Should have been more careful   And if you want a vectorised version  based on Andrie s code   substrRight  lt - function x  n     sapply x  function xx           substr xx   nchar xx -n 1   nchar xx                  gt  substrRight c  12345   ABCDE   2  12345 ABCDE   45    DE    Note that I have changed  nchar x -n  to  nchar x -n 1  to get n characters

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A little modification on  Andrie solution gives also the complement     substrR  lt - function x  n       if n  gt  0  substr x   nchar x -n 1   nchar x   else substr x  1   nchar x  n     x  lt -  moSvmC20F 5 rda  substrR x -4   1   moSvmC20F 5    That was what I was looking for  And it invites to the left side    substrL  lt - function x  n      if n  gt  0  substr x  1  n  else substr x  -n 1  nchar x     substrL substrR x -4  -2   1   SvmC20F 5

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someone before uses a similar solution to mine  but I find it easier to think as below    gt  text lt - some text in a string    we want to have only the last word  string  with 6 letter  gt  n lt -5  as the last character will be counted with nchar    here we discount 1  gt  substr x text start nchar text -n stop nchar text     This will bring the last characters as desired

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If you don t mind using the stringr package  str sub is handy because you can use negatives to count backward   x  lt -  some text in a string  str sub x -6 -1   1   string    Or  as Max points out in a comment to this answer   str sub x  start  -6   1   string

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str    This is an example  n   7 result   substr str  nchar str  1 -n nchar str   print result    gt   1   example   gt

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I m not aware of anything in base R  but it s straight-forward to make a function to do this using substr and nchar   x  lt -  some text in a string   substrRight  lt - function x  n     substr x  nchar x -n 1  nchar x      substrRight x  6   1   string   substrRight x  8   1   a string      This is vectorised  as  mdsumner points out   Consider   x  lt - c  some text in a string    I really need to learn how to count   substrRight x  6   1   string    count

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I use substr too  but in a different way  I want to extract the last 6 characters of  Give me your food   Here are the steps    1  Split the characters  splits  lt - strsplit  Give me your food    split          2  Extract the last 6 characters  tail splits  1    n 6    Output    1       f   o   o   d        Each of the character can be accessed by splits  1   x   where x is 1 to 6

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I wrote some functions that can do all of these after failing my last exam on string manipulation in R programming  If you are coming from Excel  these functions will be similar to LEFT    RIGHT    and MID   functions     This counts from the left and then extract n characters  str left  lt - function string  n      substr string  1  n         This counts from the right and then extract n characters  str right  lt - function string  n      substr string  nchar string  -  n - 1   nchar string         This extract characters from the middle  str mid  lt - function string  from   2  to   5        substr string  from  to        Examples  x  lt -  quot some text in a string quot  str left x  4   1   quot some quot   str right x  6   1   quot string quot   str mid x  6  9   1   quot text quot

[r] Extracting the last n characters from a string in R

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