Getting the output of str() and saving it to a dataframe-CodePudding

I want to have a script that will ouput the class of a variable for a dataframe. I usually use str() to do this but I realize I would like to save the results to a dataframe.

Code

str(mtcars)

> str(mtcars)
'data.frame':   32 obs. of  11 variables:
 $ mpg : num  21 21 22.8 21.4 18.7 18.1 14.3 24.4 22.8 19.2 ...
 $ cyl : num  6 6 4 6 8 6 8 4 4 6 ...
 $ disp: num  160 160 108 258 360 ...
 $ hp  : num  110 110 93 110 175 105 245 62 95 123 ...
 $ drat: num  3.9 3.9 3.85 3.08 3.15 2.76 3.21 3.69 3.92 3.92 
 $ wt  : num  2.62 2.88 2.32 3.21 3.44 ...
 $ qsec: num  16.5 17 18.6 19.4 17 ...
 $ vs  : num  0 0 1 1 0 1 0 1 1 1 ...
 $ am  : num  1 1 1 0 0 0 0 0 0 0 ...
 $ gear: num  4 4 4 3 3 3 3 4 4 4 ...
 $ carb: num  4 4 1 1 2 1 4 2 2 4 ...

Is there any easy way to save this output?

My desired output would be something like this

Colname    class
mpg         num
cyl         num
disp        num
etc..

CodePudding user response：

You can use a couple tidyverse functions: purrr::map_chr calls the class function on each column, returning a named character vector, and tibble::enframe makes a data frame out of the names and values.

tibble::enframe(purrr::map_chr(mtcars, class), name = "Colname", value = "class")
#> # A tibble: 11 × 2
#>    Colname class  
#>    <chr>   <chr>  
#>  1 mpg     numeric
#>  2 cyl     numeric
#>  3 disp    numeric
#>  4 hp      numeric
#>  5 drat    numeric
#>  6 wt      numeric
#>  7 qsec    numeric
#>  8 vs      numeric
#>  9 am      numeric
#> 10 gear    numeric
#> 11 carb    numeric

With base R functions, just create the data frame directly from the names and sapply, dropping the row names (they'll be the same as the first column)

data.frame(Colname = names(mtcars),
           class = sapply(mtcars, class),
           row.names = NULL)
# same output, just not a tibble

CodePudding user response：

We may use stack from base R on a named vector to create two column data.frame

setNames(stack(sapply(mtcars, class))[2:1], c("Colname", "class"))

-output

 Colname   class
1      mpg numeric
2      cyl numeric
3     disp numeric
4       hp numeric
5     drat numeric
6       wt numeric
7     qsec numeric
8       vs numeric
9       am numeric
10    gear numeric
11    carb numeric

Another option is from the output of str with base R

strcapture("^([^:] ):\\s (\\w ).*", trimws(capture.output(str(mtcars))[-1], 
       whitespace = "\\s \\$\\s "), 
  data.frame(Colname = character(), class = character()))

-output

 Colname class
1     mpg    num
2     cyl    num
3     disp   num
4     hp     num
5     drat   num
6     wt     num
7     qsec   num
8     vs     num
9     am     num
10    gear   num
11    carb   num