[R] applying strsplit to a whole column

[David Winsemius]

On Aug 4, 2010, at 3:31 PM, David Winsemius wrote:

>
> On Aug 4, 2010, at 3:03 PM, Dimitri Liakhovitski wrote:
>
>> I am sorry, someone said that strsplit automatically works on a
>> column. How exactly does it work?
>> For example, if I want to grab just the first (or the second) part of
>> the string in nam1 that should be split based on ".."
>> x<-data.frame(nam1=c("bbb..aba","ccc..abb","ddd..abc","eee..abd"),
>> stringsAsFactors=FALSE)
>> str(x)
>> strsplit(x[[1]],split="\\..")
>> str(strsplit(x[[1]],split="\\.."))

You should realize that the pattern "\\.." is not going to match just  
".." but rather will match ".<any-char>". To match just ".." you would  
need "\\.\\."
>>
>> I am getting a list - hence, it looks like I have to go in a loop...?

Other way with gsub:

 > gsub( "^.+\\." , "" ,  x[[1]])

# Notice that the first <dot> (in the pattern) followed by "+" will  
match
# anything up to the last <dot> (in the string)

[1] "aba" "abb" "abc" "abd"
 > gsub( "\\.\\..+$" , "" ,  x[[1]])
[1] "bbb" "ccc" "ddd" "eee"

>>
> > lapply( strsplit(x[[1]],split="\\.."), "[", 1)
> [[1]]
> [1] "bbb"
>
> [[2]]
> [1] "ccc"
>
> [[3]]
> [1] "ddd"
>
> [[4]]
> [1] "eee"
>
> > lapply( strsplit(x[[1]],split="\\.."), "[", 2)
> [[1]]
> [1] "aba"
>
> [[2]]
> [1] "abb"
>
> [[3]]
> [1] "abc"
>
> [[4]]
> [1] "abd"
>
> > unlist(lapply( strsplit(x[[1]],split="\\.."), "[", 2) )
> [1] "aba" "abb" "abc" "abd"
> > unlist(lapply( strsplit(x[[1]],split="\\.."), "[", 1) )
> [1] "bbb" "ccc" "ddd" "eee"
> >
>
>
>> Thank you!
>> Dimitri
>>
>>
>> On Wed, Aug 4, 2010 at 2:39 PM, Dimitri Liakhovitski
>> <dimitri.liakhovitski at gmail.com> wrote:
>>> Thank you very much, everyone!
>>> Dimitri
>>>
>>> On Wed, Aug 4, 2010 at 2:10 PM, David Winsemius <dwinsemius at comcast.net 
>>> > wrote:
>>>>
>>>> On Aug 4, 2010, at 1:42 PM, Dimitri Liakhovitski wrote:
>>>>
>>>>> I am sorry, I'd like to split my column ("names") such that all  
>>>>> the
>>>>> beginning of a string ("X..") is gone and only the rest of the  
>>>>> text is
>>>>> left.
>>>>
>>>> I could not tell whether it was the string "X.." or the pattern  
>>>> "X.." that
>>>> was your goal for matching and removal.
>>>>>
>>>>> x<-data.frame(names=c("X..aba","X..abb","X..abc","X..abd"))
>>>>> x$names<-as.character(x$names)
>>>>
>>>> a) Instead of "names" which is heavily used function name, use  
>>>> something
>>>> more specific. Otherwise you get:
>>>>> names(x)
>>>> "names"  # and thereby avoid list comments about canines.
>>>>
>>>> b) Instead of coercing a character vector back to a character  
>>>> vector, use
>>>> stringsAsFactors = FALSE.
>>>>
>>>>> x<-data.frame(nam1=c("X..aba","X..abb","X..abc","X..abd"),
>>>>> stringsAsFactors=FALSE)
>>>> #Thus is the pattern version:
>>>>
>>>>> x$nam1 <- gsub("X..",'', x$nam1)
>>>>> x
>>>> nam1
>>>> 1   aba
>>>> 2   abb
>>>> 3   abc
>>>> 4   abd
>>>>
>>>> This is the string version:
>>>>> x<-data.frame(nam1=c("X......aba","X.y.abb","X..abc","X..abd"),
>>>>> stringsAsFactors=FALSE)
>>>>> x$nam1 <- gsub("X\\.+",'', x$nam1)
>>>>> x
>>>>  nam1
>>>> 1   aba
>>>> 2 y.abb
>>>> 3   abc
>>>> 4   abd
>>>>
>>>>
>>>>> (x)
>>>>> str(x)
>>>>>
>>>>> Can't figure out how to apply strsplit in this situation - without
>>>>> using a loop. I hope it's possible to do it without a loop - is  
>>>>> it?
>>>>
>>>> --


David Winsemius, MD
West Hartford, CT