[R] paste first row string onto every string in column

[Jill Hollenbach]

Thanks so much everybody, this has been incredibly helpful--not only is my
immediate issue solved but I've learned a lot in the process. The lapply
solution is best for me, as I need flexibility to edit df's with varying
numbers of columns. 

Now, one more question: after appending the string from the first line, I am
manipulating the df further(recoding the original contents; this I have
working fine), and afterwards I will need to strip back off that string. It
seems relatively straightforward, except that, as shown in the example above
(df2), there is an astersik involved (I need to remove all characters up to
and including the asterisk) which seems problematic.
Any suggestions? 
Many thanks,
Jill



Don MacQueen wrote:
> 
> Let's start with something simple and relatively easy to understand, 
> since you're new to this.
> 
> First, here's an example of the core of the idea:
>>  paste('a',1:4)
> [1] "a 1" "a 2" "a 3" "a 4"
> 
> Make it a little closer to your situation:
>>  paste('a*',1:4, sep='')
> [1] "a*1" "a*2" "a*3" "a*4"
> 
> Sometimes it helps to save the number of rows in your dataframe in a 
> new variable
> 
> nr <- nrow(df)
> 
> Then, for your first column, the "a*" in the above example is df$V1[1]
> For the 1:4 in the example, you use  df$V1[ 2:nr]
> Put it together and you have:
> 
>     dfnew <- df
>     dfnew$V1[ 2:nr] <- paste( dfnew$V1[1], dfnew$V1[ 2:nr] )
> 
> But you can use "-1" instead of "2:nr", and you get
> 
>    dfnew$V1[ -1 ] <- paste( dfnew$V1[1], dfnew$V1[ -1] )
> 
> That's how you can do it one column at a time.
> Since you have only four columns, just do the same thing to V2, V3, and
> V4.
> 
> But if you want a more general method, one that works no matter how 
> many columns you have, and no matter what they are named, then you 
> can use lapply() to loop over the columns. This is what Patrick 
> Connolly suggested, which is
> 
>     as.data.frame(lapply(df, function(x) paste(x[1], x[-1], sep = "")))
> 
> Note, though, that this will do it to all columns, so if you ever 
> happen to have a dataframe where you don't want to do all columns, 
> you'll have to be a little trickier with the lapply() solution.
> 
> -Don
> 
> At 6:48 PM -0700 8/11/09, Jill Hollenbach wrote:
>>Hi,
>>I am trying to edit a data frame such that the string in the first line is
>>appended onto the beginning of each element in the subsequent rows. The
data
>>looks like this:
>>
>>>  df
>>       V1   V2   V3   V4  
>>1   DPA1* DPA1* DPB1* DPB1*
>>2   0103 0104 0401 0601
>>3   0103 0103 0301 0402
>>.
>>.
>>  and what I want is this:
>>
>>>dfnew
>>       V1   V2   V3   V4  
>>1   DPA1* DPA1* DPB1* DPB1*
>>2   DPA1*0103 DPA1*0104 DPB1*0401 DPB1*0601
>>3   DPA1*0103 DPA1*0103 DPB1*0301 DPB1*0402
>>
>>any help is much appreciated, I am new to this and struggling.
>>Jill
>>
>>___
>>  Jill Hollenbach, PhD, MPH
>>     Assistant Staff Scientist
>>     Center for Genetics
>>     Children's Hospital Oakland Research Institute
>>     jhollenbach at chori.org
>>
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>>
>>______________________________________________
>>R-help at r-project.org mailing list
>>https://*stat.ethz.ch/mailman/listinfo/r-help
>>PLEASE do read the posting guide
http://*www.*R-project.org/posting-guide.html
>>and provide commented, minimal, self-contained, reproducible code.
> 
> 
> -- 
> --------------------------------------
> Don MacQueen
> Environmental Protection Department
> Lawrence Livermore National Laboratory
> Livermore, CA, USA
> 925-423-1062
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
> 
> 

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