Fixes single column dataframe

[robne1982]

Description

Fixes #71, where the rCompare function would error if a single column dataframe was passed.

This was caused by the way R handles filtering dataframes with a single column. df[1:2, ] returns a dataframe if df has 2+ columns but returns a vector if df has 1 column.

This behaviour can be changed by passing drop=TRUE (see https://stackoverflow.com/questions/21025609/how-do-i-extract-a-single-column-from-a-data-frame-as-a-data-frame)

Motivation and Context

Fixes #71 reported by an external user

How Has This Been Tested?

• added a new end to end test that checks that the whole dataCompareR flow works for single column dataframes
• did not amend the tests for the modified matchNoIndex function because those tests look like they could use a refactor/tidy up anyway - I can go back and do this if needed?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

Tests throw existing warnings around testthat . Travis isn't happy, but that appears to be due to #76 .