CODEWITHSUNDEEP
rlistloopsdataframe
erikfjonsson
erikfjonsson

Reputation: 197

Create new column in several data frames with value dependent on name of data frame

I have several similarly named data frames in R. I am looking for a neat way to create a new column in each one of these data frames. The values in these columns should be dependent on the name of the data frame.

I have:

dfARCHIMEDES
    var1   var2
     a      b
     c      d

dfPYTHAGORAS
    var1   var2
     e      f
     g      h

And it should become:

dfARCHIMEDES
    var1   var2   newvar
     a      b      ARCHIMEDES
     c      d      ARCHIMEDES

dfPYTHAGORAS
    var1   var2   newvar
     e      f      PYTHAGORAS
     g      h      PYTHAGORAS

It goes without saying that if the data would have been this simple it would have been an easy task. However, I currently have about 250 data frames with 15 columns and 500 rows each.

I would be grateful for any help.

Upvotes: 0

Views: 39

Answers (2)

Augusto Fadel
Augusto Fadel

Reputation: 319

You can get a vector with the names of all data frame in the global environment by doing:

library(dplyr)

df_names <- 
  sapply(.GlobalEnv, is.data.frame) %>% 
  which() %>% 
  names()

After that, a loop will do the trick:

for (i in df_names) {
  assign(i, cbind(get(i), newvar = i))
}

Upvotes: 0

Roman Luštrik
Roman Luštrik

Reputation: 70643

You can approach this in the following manner. See comments in the code.

# make some sample data (which OP should provide...)
dfARCHIMEDES <- data.frame(var1 = c("a", "c"),
                           var2 = c("b", "d"))
dfPYTHAGORAS <- data.frame(var1 = c("e", "g"),
                           var2 = c("g", "h"))

# collect all object names that start with a "df" from your workspace
get.dfs <- ls(pattern ="^df")

# go through each data.frame
for (i in get.dfs) {
  tmp <- get(i) # save the data.frame into a temporary variable
  newname <- gsub("^df", "", i) # remove the df part from the name
  tmp$newvar <- newname # create new variable with the new name
  assign(i, tmp) # re-write the data.frame
}

> dfARCHIMEDES
  var1 var2     newvar
1    a    b ARCHIMEDES
2    c    d ARCHIMEDES
> dfPYTHAGORAS
  var1 var2     newvar
1    e    g PYTHAGORAS
2    g    h PYTHAGORAS

Upvotes: 2

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