R help - Mar 2012 - How to use access results of gregexpr in data frames

Hello,
I'm trying to figure out how to find the index of the second occurrence of
"/" in a string (which happens to represent a date) within a data
frame column.

I've used the following code successfully to find the first instance of
"/".


dframe <- data.frame(date=c("5/14/2011", "4/7/2011"))
dframe$x1 <- regexpr("/", dframe[, 1])
dframe 
date x1
1 5/14/2011  2
2  4/7/2011  2To find the second instance, I thought I'd try to use gregexpr
to find all instances of "/" (there's always two per string).


dframe$all <- gregexpr("/", dframe[, 1])
dframe
date x1  all
1 5/14/2011  2  2,5
2  4/7/2011  2  2,4
So far so good.  I then thought to index the second element of dframe$all.  I
tried both of the following unsuccessfully.

dframe$x2 <- dframe[, "all"][[2]]
dframe$x2 <- dframe[, "all"][2]

The desired final output is as follows ... but I don't know how to get
there.
 date  x1  all  x2
1 5/14/2011   2  2,5   5
2  4/7/2011   2  2,4   4
Many thanks for your help,
Mauricio

	[[alternative HTML version deleted]]

I think when you assign to dframe$all there's more going on than you
realize: you're actually using a multi-element list as a column of a
data frame which is, while possible, perhaps nonstandard. Perhaps you
want this:

dframe$all <- t(simplify2array(gregexpr("/", dframe[, 1])))
print(dframe)
#       date x1 all.1 all.2
# 1 5/14/2011  2     2     5
# 2  4/7/2011  2     2     4

If you just want the location of the second slash, this works:

dframe$x2 <- sapply(gregexpr("/", dframe[, 1]),`[`,2)

Hope this helps,

Michael

On Fri, Mar 30, 2012 at 7:14 PM, Mauricio Cornejo
<mauriciocornejo at yahoo.com> wrote:
> Hello,
> I'm trying to figure out how to find the index of the second occurrence
of "/" in a string (which happens to represent a date) within a data
frame column.
>
> I've used the following code successfully to find the first instance of
"/".
>
>
> dframe <- data.frame(date=c("5/14/2011",
"4/7/2011"))
> dframe$x1 <- regexpr("/", dframe[, 1])
> dframe
> date x1
> 1 5/14/2011 ?2
> 2 ?4/7/2011 ?2To find the second instance, I thought I'd try to use
gregexpr to find all instances of "/" (there's always two per
string).
>
>
> dframe$all <- gregexpr("/", dframe[, 1])
> dframe
> date x1 ?all
> 1 5/14/2011 ?2 ?2,5
> 2 ?4/7/2011 ?2 ?2,4
> So far so good.? I then thought to index the second element of dframe$all.?
I tried both of the following unsuccessfully.
>
> dframe$x2 <- dframe[, "all"][[2]]
> dframe$x2 <- dframe[, "all"][2]
>
> The desired final output is as follows ... but I don't know how to get
there.
> ?date ?x1 ?all ?x2
> 1 5/14/2011 ? 2 ?2,5 ? 5
> 2 ?4/7/2011 ? 2 ?2,4 ? 4
> Many thanks for your help,
> Mauricio
>
> ? ? ? ?[[alternative HTML version deleted]]
>
>
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