New "rename" command to change column header names

[jlumbroso]

This addresses issue #173 by introducing a new verb/command "rename" which allows renaming of all selected columns.

Implemented following exactly @BurntSushi's recommendations:

A simpler version might be too just keep the same select syntax, which selects some number of columns in a particular order. Then the remaining positional arguments are the new names of the columns, where there are exactly N arguments, where N is the number of fields selected.

The general syntax is:

xsv rename [options] [--] <selection> <renamed>... [<input>]

where first you select columns with the same syntax as the select command, and then you must provide exactly as many positional arguments to rename the selected columns. Of course, this includes the ability to copy a column multiple times with different names.

Here are some usage examples:

• Assume a file example1.csv contains the following:

  header1,header2
  row1H1,row1H2
  row2H1,row2H2
  

• Here is how we rename both columns showing different variants with the selection syntax:

  $ xsv rename 'header1,header2' H1 H2 example1.csv
  H1,H2
  row1H1,row1H2
  row2H1,row2H2
  
  $ xsv rename 1-2 H1 H2 example1.csv
  H1,H2
  row1H1,row1H2
  row2H1,row2H2
  
  $ xsv rename 1,1,1,2 H1a H1b H1c H2 example1.csv
  H1a,H1b,H1c,H2
  row1H1,row1H1,row1H1,row1H2
  row2H1,row2H1,row2H1,row2H2
  
  $ xsv rename 1-2 H1 example1.csv
  While renaming, selected 2 columns, but only provided 1 new names.
  

This also addresses one of the points of issue #96, while being not as powerful but probably cleaner/easier to compose with other operations.

AFAIK, compilation produced no warnings; I tried to respect conventions, encapsulations and modularization as much as possible. Please let me know how to improve this pull request.

[purcell]

Nice! 🎉

[purcell]

Checking back in on this, it occurs to me that the README might also need to be updated to list the new subcommand.

[shouze]

@purcell @jlumbroso coming! jlumbroso#1

[jlumbroso]

@purcell Sorry, had not seen your second comment, but you are quite right of course!
@shouze Merci Sébastien !

[geekscrapy]

Is this released? I just did a brew install and it's not included :)

[jlumbroso]

@geekscrapy No, this was never merged into the codebase by @BurntSushi. Given the growing number of pull requests that are unanswered, the lack of commits, my guess is that the original maintainer no longer has any mental bandwidth for this project.

I created my own project to address my needs; perhaps you might find it useful:
https://github.com/jlumbroso/csv-merge