Human - Readable summary of missings

[njtierney]

I need to provide key summaries of the missingness in the data for:

• cases
• variables
• data.frames

It also needs to work with group_by()

[njtierney]

At the moment miss_summary returns a tibble with lists of the other summaries.

This should change, and at the time I thought it would be useful to use list columns because they were new and a neat way of storing info. I think that miss_summary should instead be something like this:

miss_prop_summary(airquality)

# A tibble: 1 x 3
      df   var  case
   <dbl> <dbl> <dbl>
1 0.0479 0.333 0.275

But transposed:

# A tibble: 3 x 2
  type   prop_miss
  <chr>  <dbl>
1 df     0.0479
2 vars   0.333 
3 cases  0.275 

And maybe with n_miss, prop_miss.

[njtierney]

this is described in more detail in #316