How do i add column names to my for-loop in R

April 28, 2022

I made a loop to run all possible combinations of a regression model. As i only need to keep the residuals of the model i made it as such:

df <- data.frame(t(combn(colnames(orig_df), m = 2)))

test = NULL
for (i in 1:(nrow(df)-1)) {
  for (j in (i+1):nrow(df)) {
    x <- lm(orig_df[[i]] ~ orig_df[[j]], data = orig_df)
    y <- x$residuals
    test <- cbind(test, y)
  }
}

My problem, however, is adding names to the new data frame (here named "test"). I thought a good way to tell the residuals apart would be adding x$call[2].
However if i create the loop so that:

test = NULL
for (i in 1:(nrow(df)-1)) {
  for (j in (i+1):nrow(df)) {
    x <- lm(orig_df[[i]] ~ orig_df[[j]], data = Telekom)
    y <- x$residuals
    test <- cbind(test, y)
    colnames(test) <- paste(x$call[2])  
  }
}

After this the loop stops working as it should, and the error displayed is:
length of 'dimnames' [2] not equal to array extent . What is my error here?

Thanks in advance!

For first loop:

For second loop:

>Solution :

The issue can be reproduced with mtcars data

> model <- lm(mtcars[[1]] ~ mtcars[[2]])
> model$call
lm(formula = mtcars[[1]] ~ mtcars[[2]])

We may assign the call afterwards

> model$call[[2]] <- as.formula(paste0(names(mtcars)[1], "~ ", names(mtcars)[2]))
> model$call
lm(formula = mpg ~ cyl)

In the OP’s loop, may be this modification can work

test = NULL
for (i in 1:(nrow(df)-1)) {
  for (j in (i+1):nrow(df)) {
    x <- lm(orig_df[[i]] ~ orig_df[[j]], data = Telekom)
    x$call[[2]] <- as.formula(paste0(names(orig_df)[i], "~ ", names(orig_df)[j])))
    y <- x$residuals
    test <- cbind(test, y)
    colnames(test)[ncol(test)] <- paste(x$call[[2]])  
  }
}