Replace Data based on Casenumber

General
1

I have a dataset which I want to use to plot Causal Impact data using ggplot2. I want to replace the data with NA in the first 25 rows in one of the columns. Is that possible and if so, how?

2 
your_dat[1:25,3] <- NA

For the first 25 rows of column 3

3

That works like a charm. Thank you very much.