Column Name Changes in R for Loop for Defined Data Frame

How to change column names while in a loop in R?

This the approach I would take. The following script not only changes the column names, but also creates 3 dataframes in the global environment kind of like your original script.

for (i in 1:3){
  noms <- c("n1","n2","n3") # create the names in order the columns appear in the dataframe
  
  df_ <- data.frame(matrix("", nrow = 3, ncol = 3)) # create the dataframe
  
  df_nom <- paste("mydf", i, sep = "") # create the dataframe name
  
  colnames(df_) <- noms # assign the names to the columns
  
  assign(df_nom, df_) # rename the dataframe
}

loop for renaming columns in r

#sample data
set.seed(1)
df <- data.frame(id=1:4, replicate(5,sample(0:1,4,rep=TRUE)))

#define a list of varying "varname"
varname <- c('OR', 'FA')
#define how many times above "varname" repeat itself
n <- c(2, 3) #let's say that 'OR' repeats 2 times and 'FA' 3 times

#replace column name
names(df)[2:ncol(df)] <- unlist(mapply(function(x,y) paste(x, seq(1,y), sep="_"), varname, n))

Output is:

  id OR_1 OR_2 FA_1 FA_2 FA_3
1  1    0    0    1    1    1
2  2    0    1    0    0    1
3  3    1    1    0    1    0
4  4    1    1    0    0    1

Changing Column names of multiple data frames using a for loop with data frames loaded into a List

L <- lapply(L, function(x){
  colnames(x) <- c("NewName1", "NewName2")
  x
} )

Loop over a list of dataframes and change column names in R

dflist <- list(df,df2)
for (i in 1:length(dflist)) {

if(any(names(dflist[[i]]) == remNames)){
    colnames(dflist[[i]]) <- dflist[[i]][1,]
    dflist[[i]] = dflist[[i]][-1, ]
  }

}

dflist[[i]][names(dflist[[i]])] == remNames will check the enitre dataframe, hence if will return FALSE and nothing happend, consider the following example when i=2

> i=2
> dflist[[i]][names(dflist[[i]])] == remNames
        X2 X..X1
[1,] FALSE FALSE
[2,] FALSE FALSE
[3,] FALSE FALSE

A better solution is to use grepl to see if the column names contain a .. or X, so the if becomes

if(any(grepl('\\.\\.|X',names(dflist[[i]])))){...}

As to data.frame,how to loop column name first and then loop row name of column?

We loop over the columns of dataset with sapply, get the index of non-NA elements, use that to subset the row.names, paste the elements by collapseing with + and paste with the column names of 'df' with the output of sapply

paste(names(df), sapply(df, function(x) 
        paste(row.names(df)[which(!is.na(x))], collapse="+")), sep="=")
#[1] "cola=1+2+4" "colb=1+4"   "colc=2+3"  

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Or with which/arr.ind

i1 <- which(!is.na(df), arr.ind = TRUE)
paste(names(df), tapply(row.names(df)[i1[,1]], i1[,2], 
      FUN = paste, collapse="+"), sep="=")
#[1] "cola=1+2+4" "colb=1+4"   "colc=2+3"  

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Or with imap

library(purrr)
library(stringr)
unname(imap_chr(df, ~  str_c(.y, "=", 
        str_c(row.names(df)[!is.na(.x)], collapse='+'))))
#[1] "cola=1+2+4" "colb=1+4"   "colc=2+3"  

Change column names for multiple data frames in a loop

If you want to go this way you probably need the function assign. As an example:

rivers <- c("df_Main", "df_Danube", "df_Isar", "df_Inn")

for (i in rivers) {
  x=get(i)
  colnames(x) <- c("bla", "bla", "bla", "bla")
  assign(i,x)
}

If you need to do it for more than 4 data.frames maybe you should check an apply function.

Still, if you plan to plot it via ggplot2 it might be more useful to have it in a single df.

Loop through dataframe column names - R

To answer the exact question and fix the code given, see the example below

df <- iris # data

for (i in colnames(df)){
   print(class(df[[i]]))
}
# [1] "numeric"
# [1] "numeric"
# [1] "numeric"
# [1] "numeric"
# [1] "factor"

1. you need to used colnames to get the column names of df.
2. you access each column using df[[i]] if you want to know the class of that. df[i] is of class data.frame.

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