Add leading zeros to colum names-CodePudding

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!

CodePudding user response：

We can use

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

CodePudding user response：

Here is another option:

library(tidyverse)

set.seed(35)
example <- tibble(`weather 1` = runif(2),
                  `weather 2` = runif(2),
                  `weather 3` = runif(2))

rename_with(example, ~str_replace(., "(weather )(\\d )", "\\10\\2"), everything())
#> # A tibble: 2 x 3
#>   `weather 01` `weather 02` `weather 03`
#>          <dbl>        <dbl>        <dbl>
#> 1       0.857         0.553       0.486 
#> 2       0.0108        0.950       0.0939

or with base R


colnames(example) <- gsub("(weather )(\\d )", "\\10\\2", colnames(example))
example
#> # A tibble: 2 x 3
#>   `weather 01` `weather 02` `weather 03`
#>          <dbl>        <dbl>        <dbl>
#> 1       0.857         0.553       0.486 
#> 2       0.0108        0.950       0.0939