[R] String manipulation with regexpr, got to be a better way

Eik Vettorazzi E.Vettorazzi at uke.de
Fri Sep 30 10:45:06 CEST 2011

Hi Chris,
why not using routines for dates
dates <- c("09/10/2003", "10/22/2005")

or take just the last 4 chars from dates


Am 29.09.2011 16:23, schrieb Chris Conner:
> Help-Rs,
> I'm doing some string manipulation in a file where I converted a string date in mm/dd/yyyy format and returned the date yyyy.
> I've used regexpr (hat tip to Gabor G for a very nice earlier post on this function) in steps (I've un-nested the code and provided it and an example of what I did below.  My question is: is there a more efficient way to do this.  Specifically is there a way to use regexpr or some other string function to return not the first instance, but the 2nd (or for that matter 3rd, 4th or 5th instance) of a certain string?
>  #first find the first occurence of "/" and create a variable for this firstslash <- unlist(regexpr("/", dates, fixed = TRUE)) #then use frist/ to cut the string field into an intermediate variable e.g., from 1/1/2008 to 1/2008. step1 <- substr( dates,  (firstslash + 1), nchar(dates) ) #then repeat steps 1 and 2...there's got to be a better way step2 <- unlist(regexpr("/", step1, fixed = TRUE)) #then use step2 to cut string into final product e.g., from 1/2008 to 2008. final <- substring(step1,step2 + 1, nchar(step1) )
> Thx!
> C
> 	[[alternative HTML version deleted]]
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Eik Vettorazzi
Institut für Medizinische Biometrie und Epidemiologie
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