R help - Mar 2012 - how to match exact phrase using gsub (or similar function)

trying to switch out addresses that have double directions, such as the
following example:

a = "S S Main St & Interstate 95"

a = gsub(pattern="S S ", replacement="S ", a)


… the problem is that I don't want to affect instances where this might be
a correct address such as the following:


"3421 BIGS St"


what I want to say is switch out only if this is either of the following
situations


[beginning of char]S S"

" S S "

"S S[end of char]


Is there anyway of making gsub or a similar function make the replacements
I want?  Thanks in advance for your help.


~Markus

	[[alternative HTML version deleted]]

In most regexs the carrot( ^ ) signifies the start of a line and the
dollar sign ( $ ) signifies the end.

gsub('^S S', 'S', a)

gsub('^S S', 'S', '3421 BIGS St')

you can use logical or inside your pattern too:

gsub('^S S|S S$| S S ', 'S', a)

the " S S " condition is difficult.

gsub('^S S|S S$| S S ', 'S', 'foo S S bar')

gives the wrong output. as does:

gsub('^S S | S S$| S S ', ' S ', 'foo S S bar')
gsub('^S S | S S$| S S ', ' S ', a)


so you might have to catch that with a second gsub.

gsub(' S S ', ' S ', 'foo S S bar')


On Wed, Mar 28, 2012 at 12:32 PM, Markus Weisner <r at themarkus.com>
wrote:
> trying to switch out addresses that have double directions, such as the
> following example:
>
> a = "S S Main St & Interstate 95"
>
> a = gsub(pattern="S S ", replacement="S ", a)
>
>
> ? the problem is that I don't want to affect instances where this might
be
> a correct address such as the following:
>
>
> "3421 BIGS St"
>
>
> what I want to say is switch out only if this is either of the following
> situations
>
>
> [beginning of char]S S"
>
> " S S "
>
> "S S[end of char]
>
>
> Is there anyway of making gsub or a similar function make the replacements
> I want? ?Thanks in advance for your help.
>
>
> ~Markus
>
> ? ? ? ?[[alternative HTML version deleted]]
>
>
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