Code Breaking When Turned Into Custom Function? - r

Question

I am putting together a summary table from a larger data frame. I noticed that I was re-using the following code but with different %like% characters:
# This code creates a df of values where the row name matches the character
df <- (data[which(data$`col_name` %like% "Total"),])
df <- df[3:ncol(df)]
df[is.na(df)] <- 0
# This creates a row composed of the sum of each column
for (i in seq_along(df)) {
df[10, i] <- sum(df[i])
}
# This inserts the resulting values into a separate summary table
summary[1, 2:ncol(summary)] <- df[nrow(df),]
To keep the code dry and avoid repetition, I thought it would be best to translate this into a custom function that I could then call with different strings:
create_row <- function(x) {
df <- (data[which(data$`Crop year` %like% as.character(x)),])
df <- df[3:ncol(df)]
df[is.na(df)] <- 0
for (i in seq_along(df)) {
df[10, i] <- sum(df[i])
}
}
# Then populate the summary table as before with the results
total <- create_row("Total")
summary[1, 2:ncol(summary)] <- total[nrow(total),]
However when attempting to run this, it simply returns an empty variable.
Through trial and error, I have found that the line of code causing this is:
df[is.na(df)] <- 0
The code works absolutely fine when run line by line outside of this custom function.

Answer 1

As mentioned in the comments if you add return(df) at the end of the function, the function will work. We need to do that because for loop unlike any other functions doesn't return an object after it's executed.
Moreover, as mentioned in the comments by #alan that you can use colSums to get sum of each column directly instead of for loop to loop over each column and take its sum.