Append all column names in multiple data.frames in a loop

Question

I have multiple data.frames that all have different names but same column names, for example:

filenames <- c(1:10)
for (i in filenames){
  filenames[i] <- paste("df",filenames[i],sep="")  
  assign((filenames[i]), data.frame(matrix(rnorm(20), nrow=10)))
  }

How can one append the column names within each df with the name of that df?

The output would be:

> head(df1)
      df1_X1     df1_X2
1  0.2343486  0.2191546
2  0.5042413  2.0720167
3 -0.1082240  0.7376801
4  0.2346395  0.4677974
5  1.1559909 -1.1432890
6 -1.5554426 -0.2309197
> head(df2)
       df2_X1     df2_X2
1 -2.79824632 -0.1879618
2  1.93410571  0.3012066
3  0.72948663  0.2139871
4  0.59290004  1.1093813
5  0.04826737 -0.4062374
6 -0.78271090 -1.2870127

etc...

Here is my initial solution, which does not work:

for (i in length(filenames)){  
  colnames(filenames[i]) <- paste(filenames[i], colnames(filenames[i]), sep = "_") 
}

joran · Accepted Answer · 2014-08-25 17:55:11Z

2

It is clearer and cleaner to do this with the data frames in a list. Then there's no need for awkward uses of assign, get, etc.

df1 <- data.frame(X1=1:5, X2=6:10)
df2 <- data.frame(X1=16:20, X2=21:25)

dfs <- list(df1 = df1,df2 = df2)

dfs_new <- lapply(names(dfs),
                  function(x) setNames(dfs[[x]],paste(x,colnames(dfs[[x]]),
                                                      sep = "_")))

answered Aug 25, 2014 at 17:55

joran

175k34 gold badges439 silver badges485 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Rich Scriven Over a year ago

That's what I was shooting for...couldn't quite get there.

USER_1 Over a year ago

That's a nice solution, but I would like to keep individual data frames and not coerce to a list object. Of course one could then do: df <- do.call(rbind.data.frame, dfs_new) but that gives all in one df.

akrun · Accepted Answer · 2014-08-26 04:03:48Z

1

One way would be:

 df1 <- data.frame(X1=1:5, X2=6:10)
 df2 <- data.frame(X1=16:20, X2=21:25)
 name1 <- ls(pattern="^df\\d+$") 
 cNames <- colnames(df1) #assuming that column names are the same for all dataframes

 for(i in 1:2){
  assign(name1[i], `names<-` (get(name1[i]), paste(name1[i],cNames, sep="_"))) 
  }

 df1
 # df1_X1 df1_X2
 #1      1      6
 #2      2      7
 #3      3      8
 #4      4      9
 #5      5     10

 df2
 #  df2_X1 df2_X2
 #1     16     21
 #2     17     22
 #3     18     23
 #4     19     24
 #5     20     25

Or

  cNames1 <- c(t(outer(name1, cNames, FUN=paste, sep="_")))
  names2 <- split(cNames1,gsub("_.*", "", cNames1))
  list2env(
       Map(function(n1, data) {
       names(data) <- n1
       data
      }, names2, mget(name1)),
               envir = .GlobalEnv)
  df1
 #  df1_X1 df1_X2
 #1      1      6
 #2      2      7
 #3      3      8
 #4      4      9
 #5      5     10

edited Aug 26, 2014 at 4:03

answered Aug 25, 2014 at 17:42

akrun

891k38 gold badges590 silver badges700 bronze badges

2 Comments

USER_1 Over a year ago

Thanks. Works fine. Why use 'names<-'? It's the first time I see this kind of assignment operator in R.

akrun Over a year ago

@USER52306 It is almost similar to x <- get(name1[i]); names(x) <- paste(name1[i], cNames, sep="_"); assign(name1[i], x)

Collectives™ on Stack Overflow

Append all column names in multiple data.frames in a loop

2 Answers 2

2 Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related