[R] convert 'character' vector containing mixed formats to 'Date'

[Liviu Andronic]

Dear all
I have a 'character' vector containing mixed formats (thanks Excel!)
and I'd like to translate it into a default "%Y-%m-%d" Date vector.
x <- c("1/3/2005", "13/04/2004", "2/5/2005", "2/5/2005", "7/5/2007",
       "22/04/2004", "21/04/2005", "20080430", "13/05/2003", "20080529",
       NA, NA, "19/05/1999", "17/05/2000", "17/05/2000")


In the above you will see that some dates are of format="%d/%m/%Y",
others of format="%Y%m%d" and some NA values. Can you suggest a
straight-forward way of transforming these to a uniform 'character' or
'Date' vector? I tried to do the following, but it outputs very
strange results:
> x
 [1] "1/3/2005"   "13/04/2004" "2/5/2005"   "2/5/2005"   "7/5/2007"
"22/04/2004"
 [7] "21/04/2005" "20080430"   "13/05/2003" "20080529"   NA
NA
[13] "19/05/1999" "17/05/2000" "17/05/2000"
> sum(xa <- grepl('/', x))
[1] 11
> sum(xb  <- grepl('200', substr(x, 1,4)))
[1] 2
> sum(xc <- is.na(x))
[1] 2
> x[xa] <- as.Date(x[xa], format="%d/%m/%Y")
> x[xb] <- as.Date(x[xb], format="%Y%m%d")
> x
 [1] "12843" "12521" "12905" "12905" "13640" "12530" "12894" "13999"
"12185" "14028"
[11] NA      NA      "10730" "11094" "11094"


The culprit is likely that the 'x' vector is 'character' throughout,
but I'm not sure how to work around. For example, I couldn't figure
how to create an empty 'Date' vector. Regards
Liviu


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