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 <- 'hello stackoverflow'
I'd like to be able to do something like this:
a <- x.pop[1]
print(a)
'h'
print(x)
'ello stackoverflow'
There is also str_sub
from the stringr package
x <- 'hello stackoverflow'
str_sub(x, 2) # or
str_sub(x, 2, str_length(x))
[1] "ello stackoverflow"
removing first characters:
x <- '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)
Another alternative is to use capturing sub-expressions with the regular expression functions regmatches
and regexec
.
# the original example
x <- 'hello stackoverflow'
# grab the substrings
myStrings <- 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 <- c('hello stackoverflow', 'right back', 'at yah')
# grab the substrings
myStrings <- 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 <- sapply(myStrings, "[", 2)
myFirstStrings
[1] "h" "r" "a"
mySecondStrings <- sapply(myStrings, "[", 3)
mySecondStrings
[1] "ello stackoverflow" "ight back" "t yah"
Use this function from stringi
package
> x <- 'hello stackoverflow'
> stri_sub(x,2)
[1] "ello stackoverflow"
substring
is definitely best, but here's one strsplit
alternative, since I haven't seen one yet.
> x <- 'hello stackoverflow'
> strsplit(x, '')[[1]][1]
## [1] "h"
or equivalently
> unlist(strsplit(x, ''))[1]
## [1] "h"
And you can paste
the rest of the string back together.
> paste0(strsplit(x, '')[[1]][-1], collapse = '')
## [1] "ello stackoverflow"
Source: Stackoverflow.com