Add metadata macros

[pdeffebach]

Description of API to come

[pdeffebach]

@bkamins

This is ready for a review.

The API is very minimal. However I do add two functions, printlabels and printnotes because working with metadata in data cleaning is pretty frustrating without them.

Maybe we can have printlabels and printnotes live in DataFrames.jl?

[bkamins]

I agree here, but then maybe add a comment how to remove a note from a column?

[bkamins]

Thank you. Looks good. I would leave printlabels and printnotes in DataFramesMeta.jl for now as they are only printing things (not returning a value).

[pdeffebach]

@bkamins

I beefed up the printing a little, trying to make it as useful as possible.

We can change the API at 1.0 if people don't like it. But I think it's pretty useful.

This is ready for merging.

API of printing:

Labels

printlabels(df, [cols=All()]; unlabelled = true)

Pretty-print all labels in a data frame.

Arguments

• cols: Optional argument to select columns to print. Can
  be any valid multi-column selector, such as Not(...),
  Between(...), or a regular expression.

• unlabelled: Keyword argument for whether to print
  the columns without user-defined labels. Deftaults to true.
  For column col without a user-defined label, label(df, col) returns
  the name of the column, col.

Examples

julia> df = DataFrame(wage = [12], age = [23]);

julia> @label! df :wage = "Hourly wage (2015 USD)";

julia> printlabels(df)
┌────────┬────────────────────────┐
│ Column │                  Label │
├────────┼────────────────────────┤
│   wage │ Hourly wage (2015 USD) │
│    age │                    age │
└────────┴────────────────────────┘

julia> printlabels(df, :wage)
┌────────┬────────────────────────┐
│ Column │                  Label │
├────────┼────────────────────────┤
│   wage │ Hourly wage (2015 USD) │
└────────┴────────────────────────┘

julia> printlabels(df; unlabelled = false)
┌────────┬────────────────────────┐
│ Column │                  Label │
├────────┼────────────────────────┤
│   wage │ Hourly wage (2015 USD) │
└────────┴────────────────────────┘

julia> printlabels(df, r"^wage")
┌────────┬────────────────────────┐
│ Column │                  Label │
├────────┼────────────────────────┤
│   wage │ Hourly wage (2015 USD) │
└────────┴────────────────────────┘

Notes

printnotes(df, cols = All(); unnoted = false)

Print the notes and labels in a data frame.

Arguments

• cols: Optional argument to select columns to print. Can
  be any valid multi-column selector, such as Not(...),
  Between(...), or a regular expression.
• unnoted: Keyword argument for whether to print
  the columns without user-defined notes or labels.

For the purposes of printing, column labels are printed in
addition to notes. However column labels are not returned by
note(df, col).

julia> df = DataFrame(wage = [12], age = [23]);

julia> @label! df :age = "Age (years)";

julia> @note! df :wage = "Derived from American Community Survey";

julia> @note! df :wage = "Missing values imputed as 0 wage";

julia> @label! df :wage = "Hourly wage (2015 USD)";

julia> printnotes(df)
Column: wage
────────────
Label: Hourly wage (2015 USD)
Derived from American Community Survey
Missing values imputed as 0 wage

Column: age
───────────
Label: Age (years)

[bkamins]

Looks good. Just merge conflicts need to be resolved.

[pdeffebach]

Thanks! Will merge!