Transform R dataframes using variables in loop

Question

I am trying to replace values in a R dataframe by column. I would like to loop though a given list of columns of the dataframe and replace all "Yes" values by 1 and all the other values by 0.

I tried to do this using transform() and ifelse() functions with the something like this:

# List of selected Columns:
ColumnNames = c("Frigori", "Microond" , "Arca", "Aspira")

# Replace Values in dataframe
for(i in 1:length(ColumnNames)){
dataframe <- transform(dataframe, ColumnNames[i] = ifelse(Columnames[i] == "Yes", 1, 0))
}

This piece of code works fine with explicit column names outside the loop, but with the array it will give me the following error:

Error: unexpected '=' in:
"for(i in 1:length(Appliances)){
dataframe <- transform(dataframe, ColumnNames[i] ="

I don't know what goes wrong here, but the problem has to be related with the variable substitution.

Answer 1

The code can actually be simplified to one short line with no loops or apply() at all:

dataframe <- data.frame(a = c("No", "Yes", "No", "No", "Yes"),
                        b = c("Hi", "Hi", "Mom", "Hi", "Mom"),
                        c = c("Yes", "Yes", "Yes", "Yes", "No"))
cols <- c("a","c")
dataframe[,cols] <- as.numeric(dataframe[,cols]=="Yes")
dataframe

  a   b c
1 0  Hi 1
2 1  Hi 1
3 0 Mom 1
4 0  Hi 1
5 1 Mom 0

Answer 2

Simulated data:

data <- data.frame(matrix(ifelse(runif(40)>.5,"YES",letters[1:26]), 10, 4))

Suppose you want to change columns X2 and X4

cols <- c("X2","X4")
data[,cols] <- apply(data[cols],2,function(x) ifelse(x=="YES",1,0))