Getting and removing the first character of a string

Question

I would like to do some 2-dimensional walks using strings of characters by assigning different values to each character   I was planning to  pop  the first character of a string  use it  and repeat for the rest of the string   How can I achieve something like this   x  lt -  hello stackoverflow    I d like to be able to do something like this   a  lt - x pop 1   print a    h  print x    ello stackoverflow

User · Answer

Use this function from stringi package   gt  x  lt -  hello stackoverflow   gt  stri sub x 2   1   ello stackoverflow

User · Answer

substring is definitely best  but here s one strsplit alternative  since I haven t seen one yet    gt  x  lt -  hello stackoverflow   gt  strsplit x       1   1      1   h    or equivalently   gt  unlist strsplit x       1      1   h    And you can paste the rest of the string back together    gt  paste0 strsplit x       1   -1   collapse           1   ello stackoverflow

User · Answer

See  substring   x  lt -  hello stackoverflow  substring x  1  1      1   h  substring x  2      1   ello stackoverflow      The idea of having a pop method that both returns a value and has a side effect of updating the data stored in x is very much a concept from object-oriented programming   So rather than defining a pop function to operate on character vectors  we can make a reference class with a pop method   PopStringFactory  lt - setRefClass     PopString     fields   list      x    character           methods   list      initialize   function x              x  lt  lt - x            pop   function n   1              if nchar x     0                  warning  Nothing to pop            return                   first  lt - substring x  1  n        x  lt  lt - substring x  n   1        first              x  lt - PopStringFactory new  hello stackoverflow   x    Reference class object of class  PopString     Field  x       1   hello stackoverflow  replicate nchar x x   x pop        1   h   e   l   l   o       s   t   a   c   k   o   v   e   r   f   l   o   w

User · Answer

removing first characters    x  lt -  hello stackoverflow  substring x  2  nchar x     Idea is select all characters starting from 2 to number of characters in x  This is important when you have unequal number of characters in word or phrase    Selecting the first letter is trivial as previous answers   substring x 1 1

User · Answer

Another alternative is to use capturing sub-expressions with the regular expression functions regmatches and regexec     the original example x  lt -  hello stackoverflow     grab the substrings myStrings  lt - regmatches x  regexec             x     This returns the entire string  the first character  and the  popped  result in a list of length 1   myStrings   1    1   hello stackoverflow   h                     ello stackoverflow     which is equivalent to list c x  substr x  1  1   substr x  2  nchar x      That is  it contains the super set of the desired elements as well as the full string      Adding sapply will allow this method to work for a character vector of length   1     a slightly more interesting example xx  lt - c  hello stackoverflow    right back    at yah      grab the substrings myStrings  lt - regmatches x  regexec             xx     This returns a list with the matched full string as the first element and the matching subexpressions captured by    as the following elements  So in the regular expression                  matches the first character and      matches the remaining characters   myStrings   1    1   hello stackoverflow   h                     ello stackoverflow      2    1   right back   r            ight back      3    1   at yah   a        t yah     Now  we can use the trusty sapply     method to pull out the desired substrings   myFirstStrings  lt - sapply myStrings       2  myFirstStrings  1   h   r   a  mySecondStrings  lt - sapply myStrings       3  mySecondStrings  1   ello stackoverflow   ight back            t yah

User · Answer

There is also str sub from the stringr package  x  lt -  hello stackoverflow  str sub x  2    or str sub x  2  str length x    1   ello stackoverflow

[string] Getting and removing the first character of a string

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