Loop through list of data frames

Question

I have several data frames. In each data frame there is a column called Current.Net.Price . I want to change the column names to different names. Therefore I have two lists:

Names <- c("name1","name2","name3","name4","name5")
dfList <- list(df1,df2,df3,df4,df5)

I tried something like this:

i=1
for (df in dfList) {
  names(df)[names(df) == "Current.Net.Price"] <- Names[i]
  i<-i+1
}

But when I call

View(dfList$df2)

the column is still named Current.Net.Price

Could someone help me please? :)

for clarification: each data.frame in dfList has got a column named "Current.Net.Price" and each of those column names is to be replaced with a different name obtained from Names, right? — Tedil
– Tedil, Commented Aug 14, 2015 at 10:15
Is it me, or does this sound like an XY problem? What are you ultimately trying to solve/achieve? — Heroka
– Heroka, Commented Aug 14, 2015 at 11:00
But if this is really what you want: df[,Names(i)] <- df$Current.Net.Price. Easier to check if you make a new column and no overwriting of original data. — Heroka
– Heroka, Commented Aug 14, 2015 at 11:03
Well, it is about some price lists of different months. In each is a price and I want to rename them because at the end I would like to merge all data frames. But your solution also works :) — WinterMensch
– WinterMensch, Commented Aug 14, 2015 at 11:15

AntoniosK · Accepted Answer · 2015-08-14 11:01:08Z

3

Check this simple but similar example. It's all about how you access your dfList to exctract info about the data.frames's names.

 # data frames
dt1 = data.frame(x = 1:3,
                     y = 5:7)

dt2 = data.frame(x = 1:4,
                     z = 5:8)

dt3 = data.frame(y = 1:10,
                 x = 21:30)


Names = c("A","B","C")
dfList <- list(dt1,dt2,dt3)


for (i in 1:length(dfList)) {

  names(dfList[[i]])[names(dfList[[i]])=="x"] = Names[i]

}

answered Aug 14, 2015 at 11:01

AntoniosK

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Comments

Josh · Accepted Answer · 2015-08-14 11:03:22Z

I believe when you loop like that (loop over items in a list/vector), the original objects don't get updated. E.g.,

l <- 1:5
for (i in l) {
  i <- 3
}
l
# [1] 1 2 3 4 5

The following works for me.

df1 <- data.frame("x" = rnorm(5),"Current.Net.Price"=1:5)
df2 <- data.frame("x" = rnorm(5),"Current.Net.Price"=1:5)
df3 <- data.frame("x" = rnorm(5),"Current.Net.Price"=1:5)
df4 <- data.frame("x" = rnorm(5),"Current.Net.Price"=1:5)
df5 <- data.frame("x" = rnorm(5),"Current.Net.Price"=1:5)

Names <- c("name1","name2","name3","name4","name5")
dfList <- list(df1=df1,df2=df2,df3=df3,df4=df4,df5=df5)


for (i in 1:5) {
  names(dfList[[i]])[names(dfList[[i]]) == "Current.Net.Price"] <- Names[i]
}

sapply(dfList, colnames)

#      df1     df2     df3     df4     df5
# [1,] "x"     "x"     "x"     "x"     "x"
# [2,] "name1" "name2" "name3" "name4" "name5"

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