Question

I wrote code to extract the date from a given string. Given

  > "Date: 2012-07-29, 12:59AM PDT"

it extracts

  > "2012-07-29" 

The problem is my code looks lengthy and cumbersome to read. I was wondering if was a more elegant way of doing this.

  raw_date = "Date: 2012-07-29, 12:59AM PDT"

  #extract the string from raw date
  index = regexpr("[0-9]{4}-[0-9]{2}-[0-9]{2}", raw_date) #returns 'start' and 'end' to be used in substring

  start = index #start represents the character position 's'. start+1 represents '='
  end = attr(index, "match.length")+start-1
  date = substr(raw_date,start,end); date

Answer 1

You can use strptime() to parse time objects:

R> strptime("Date: 2012-07-29, 11:59AM PDT", "Date: %Y-%m-%d, %I:%M%p", tz="PDT")
[1] "2012-07-29 11:59:00 PDT"
R> 

Note that I shifted your input string as I am unsure that 12:59AM exists… Just to prove the point, shifted by three hours (expressed in seconds, the base units):

R> strptime("Date: 2012-07-29, 11:59AM PDT", 
+>          "Date: %Y-%m-%d, %I:%M%p", tz="PDT") + 60*60*3
[1] "2012-07-29 14:59:00 PDT"
R> 

Oh, and if you just want the date, it is of course even simpler:

R> as.Date(strptime("Date: 2012-07-29, 11:59AM PDT", "Date: %Y-%m-%d"))
[1] "2012-07-29"
R>