Loop through dataframe column names - R

Question

I'm trying to loop through the columns names of a dataframe, and evaluate which class is each column.

for (i in columns(df)){
  class(df$i)
}

I have tried everything, except the right way..

PS: I'm trying to do in this way because after I have to put different conditions for each class.

Solution

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.

Comments

[Sathish]

sapply(df, class)

[Jorge]

for (i in 1:length(df)){ class(df[,i]) }

[hpesoj626]

I don't know what operations you want to do later, but are you familiar with dplyr::mutate_if or dplyr::summarise_if sets of functions?

[viridius]

Is it possible to begin looping on a different column (e.g., column 11) other than the first column?

[Christopher Moore]

Please provide some explanation to go with this code.