Add leading zeros to colum names

Question

I'm surprised to find no one asked this question on Stackoverflow before. Maybe it's too stupid to ask?

So I have a dataframe that contains 48 weather variables, each representing a weather value for a month. I have drawn a simplified table shown below:

weather 1	weather 2	weather 3	weather 4	weather 5	weather 6	weather 7	weather 8	weather 9	weather 10	weather 11	weather 12
12	6	34	9	100	.01	-4	38	64	77	21	34
99	42	-3	34	34	.5	27	19	7	18	NA	20

My objective is to make the column names from "weather 1, weather 2, ..." to "weather 01, weather 02, ...." And I wrote a loop like this:

for (i in 1:9){
  colnames(df) = gsub(i, 0+i, colnames(df))
}

However, instead of replacing the single-digit numbers with a leading zero, R replaced the actual letter "i" with "0+i". Can anyone let me know what's going on here and how to fix it? Or is there a better way to add leading zeros to column names?

Thank you very much!

Answer 1

We can use

library(stringr)
colnames(df) <- str_replace(colnames(df), "\\d+", 
      function(x) sprintf("%02d", as.integer(x)))