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print dataframe names in loop

8 messages · Kai Mx, Jim Lemon, Omar André Gonzáles Díaz +2 more

Original
Kai Mx
# 
Hi everybody,

I just can't  figure this out:

I have a loop trough several dataframes such as

for (df in list(df1, df2, df3, ...)) {
..some functions with df..
}

now I want to print out the current dataframes name (ie the list items
name) with the cat command before the actual functions to have better
orientation in the output.
However, I haven't been successful with different variations of deparse(),
substitute(), (cat(substitute(df)) gives me 'df' for the whole loop).

Could somebody please enlighten me?

Thanks so much!

Best,

Kai
Jim Lemon
# 
Hi Kai,
One way is to name the components of your list with the names of the
data frames:

df1<-data.frame(a=1:3)
df2<-data.frame(a=4:6)
df3<-data.frame(a=7:9)
dflist<-list(df1,df2,df3)
names(dflist)<-c("df1","df2","df3")
for(i in 1:length(dflist)) cat(names(dflist)[i],"\n")
df1
df2
df3

Jim
On Fri, May 15, 2015 at 10:05 PM, Kai Mx <govokai at gmail.com> wrote:
David Winsemius
#
On May 15, 2015, at 5:05 AM, Kai Mx wrote:

            

      
      
      
    

        
You were close. Try:

 deparse(substitute(df))

            

      
      
      
    

        

      
      
    

        
David Winsemius
Alameda, CA, USA

  
  


  


      

    

    

      
      

        


  

        

      Kai Mx
    

    

      
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thanks, that would work, but isn't there a maybe more elegant way to
"extract" the name from the df variable within the current for (df in
list()) loop?

Best,

Kai

        
On Fri, May 15, 2015 at 2:20 PM, Jim Lemon <drjimlemon at gmail.com> wrote:

        

            

      
      
      
    

        

      
      
    

        

      
      
    

        

  
  


  


      

    

    

      
      

        


  

        

      Omar André Gonzáles Díaz
    

    

      
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Two seconds using google:

http://stackoverflow.com/questions/9002227/how-to-get-the-name-of-a-data-frame-within-a-list

2015-05-15 7:20 GMT-05:00 Jim Lemon <drjimlemon at gmail.com>:

            

      
      
      
    

        

      
      
    

        

      
      
    

        

  
  


  


      

    

    

      
      

        


  

        

      David Winsemius
    

    

      
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On May 15, 2015, at 10:05 AM, Kai Mx wrote:

        

            

      
      
      
    

        
You do realize that the `for` function returns NULL, I hope? I was surprised when I learned this, although it is clearly stated in the help page.

Neither `lapply` nor `for` passes the names into the environment for evaluation:

for( d in dflist ) { z <- deparse(substitute(d)); print(z)}
[1] "d"
[1] "d"
[1] "d"

People would generally use this approach:

for (n in names(dflist) { ...do something with nm or dflist[[nm]]... }

-- 
David.

            

      
      
      
    

        

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      William Dunlap
    

    

      
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You can automate the adding of the names to the list with the following
function, so you
can replace the
  dflist<-list(df1,df2,df3)
  names(dflist)<-c("df1","df2","df3")
with
  dflist <- namedList(df1, df2, df3)
If you supply names, such in
  dflist <- namedList(df1, Second=df2, log(df3))
it will use your names and create names for the unnamed ones.

(Once you make a named list of data.frames, you can remove the the
originals from your global environment so you will have a single version
of truth.)

namedList <- function (...)
{
    L <- list(...)
    nms <- names(L)
    if (is.null(nms)) {
        nms <- rep("", length(L))
    }
    if (any(needsName <- is.na(nms) | !nzchar(nms))) {
        nms[needsName] <- vapply(substitute(...())[needsName],
            function(x) deparse(x, nlines = 1L), FUN.VALUE = "")
        names(L) <- nms
    }
    L
}


Bill Dunlap
TIBCO Software
wdunlap tibco.com

        
On Fri, May 15, 2015 at 5:20 AM, Jim Lemon <drjimlemon at gmail.com> wrote:

        

            

      
      
      
    

        

      
      
    

        

      
      
    

        

  
  


  


      

    

    

      
      

        


  

        

      Kai Mx
    

    

      
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Thanks for all the input.
It seems like there is no way around introducing names for the list items,
but the namedList-function is really neat.
Function returns are not at issue for me, I rather want to use it on plots
or outputs in the console.

Best,

Kai

        
On Fri, May 15, 2015 at 10:51 PM, William Dunlap <wdunlap at tibco.com> wrote: