[R] Function for trim blanks from a string(s)?

[Prof Brian Ripley]

I am sure Marc knows that ?sub has examples of trimming trailing space and 
whitespace in various styles.

On Mon, 6 Aug 2007, Marc Schwartz wrote:

> On Mon, 2007-08-06 at 12:15 -0700, adiamond wrote:
>> I feel like an idiot posting this because every language I've ever seen has a
>> string function that trims blanks off strings (off the front or back or
>> both).

Some very common languages do not, though.  It is an exercise in Kernighan 
& Ritchie (the original C reference), and an FAQ entry for Perl.

>> Ideally, it would process whole data frames/matrices etc but I don't
>> even see one that processes a single string.  But I've searched and I don't
>> even see that.  There's a strtrim function but it does something completely
>> different.
>
> If you want to do this while initially importing the data into R using
> one of the read.table() family of functions, see the 'strip.white'
> argument in ?read.table, which would do an entire data frame in one
> call.
>
> Otherwise, the easiest way to do it would be to use sub() or gsub()
> along the lines of the following:
>
> # Strip leading space
> sub("^ +", "", YourTextVector)
>
>
> # Strip trailing space
> sub(" +$", "", YourTextVector)
>
>
> # Strip both
> gsub("(^ +)|( +$)", "", YourTextVector)
>
>
>
>
> Examples of use:
>
>> sub("^ +", "", "   Leading Space")
> [1] "Leading Space"
>
>
>> sub(" +$", "", "Trailing Space    ")
> [1] "Trailing Space"
>
>
>> gsub("(^ +)|( +$)", "", "    Leading and Trailing Space    ")
> [1] "Leading and Trailing Space"
>
>
> See ?sub which also has ?gsub
>
> Note that the above will only strip spaces, not all white space.
>
> You can then use the appropriate call in one of the *apply() family of
> functions to loop over columns/rows as may be appropriate.

Well, arrays are vectors and so can be done by

A[] <- sub(....., A)

and data frames with character columns by

A[] <- lapply(A, function(x) sub(....., x))

> HTH,
>
> Marc Schwartz
>
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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