CODEWITHSUNDEEP
rfor-loopdataframerename
user3620237
user3620237

Reputation:

R rename variables in loop with names()

In R, I have several data frames with the same structure (3 columns and several rows). All data frames follow the same naming conventions and have the same data structure, so they can be listed with an ls(pattern="NamePrefix") call.

I wanted to use a for loop to rename the second and third variable of all those data frames. Here is the code that I tried:

for (i in ls(pattern="NamePrefix"))
{
    names(i)[[2]] <- "NewName"
    names(i)[[3]] <- "OtherNewName"
}

I have also tried setting the names of the data frames as list first (by File_List <- ls(pattern="NamePrefix")) and then using that list in the loop (for (i in File_List)), but that doesn't work either.

Whatever I do, I get this error:

Error in names(i)[[2]] <- "NewName" :
'names' attribute [2] must be the same length as the vector [1]

However, if I simply do names(SomeDataset)[[2]] <- "NewName" that works perfectly. Yet somehow the for loop appears incapable of running it.

Any ideas as to why does it happen and how to fix it? Note that I am well aware of several other alternatives to do the same loop renaming over several data frames without using names(), but this was a far simpler, more intuitive alternative (I thought) and I can't see why the loop seems incapable of implementing it. So, now I want to understand why the solution that I thought was the simplest appears to be wrong (and if possible, how to fix it so that it works).

Thanks in advance!

Upvotes: 1

Views: 12406

Answers (2)

Ben Bolker
Ben Bolker

Reputation: 226182

Because i will be a character object naming the object, not the object itself. I can't actually think of a nice way to do this; the general advice for "how do I do xxxx to a bunch of objects that are all named similarly?" is "store those objects in a list" ...

dd <- data.frame(a=1,b=2,c=3)
for (i in ls(pattern="^dd")) {
    g <- get(i)
    names(g)[2:3] <- c("NewName","OtherNewName")
    assign(i,g)
}

There's probably also a solution based on (ugh) eval(parse(...))

Upvotes: 3

Diego Rodrigues
Diego Rodrigues

Reputation: 864

#Creating data frames
df1 <- data.frame("V1"=rnorm(10,1,10),"V2"=rnorm(10,1,10),"V3"=rnorm(10,1,10))
df2 <- data.frame("V1"=rnorm(10,1,10),"V2"=rnorm(10,1,10),"V3"=rnorm(10,1,10))
df3 <- data.frame("V1"=rnorm(10,1,10),"V2"=rnorm(10,1,10),"V3"=rnorm(10,1,10))
df4 <- data.frame("V1"=rnorm(10,1,10),"V2"=rnorm(10,1,10),"V3"=rnorm(10,1,10))
df5 <- data.frame("V1"=rnorm(10,1,10),"V2"=rnorm(10,1,10),"V3"=rnorm(10,1,10))

# Creating a list of data frames
df_list <- ls(pattern="df")

# Renaming the variables in the data frame
for(i in df_list){
  aux <- get(i)
  names(aux)[2:3] <- c("Vari2","Vari3")
  assign(i,aux)
}

Upvotes: 3

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