tif 0.3.0

Further discussion has lead us to simplify the corpus and token data frame formats. The doc_id, text, and token columns can be in any position within the data frame.

tif 0.2.0

After a round of input for the initial version of the specification, we decided to allow two formats for corpus and tokens objects. In addition to the original data frame variants there is a character vector corpus object and a list-based tokens object. Converts between the various types are now included in the package.

tif_is_corpus_character returns TRUE or FALSE for whether the input is a valid character vector corpus object.
tif_is_tokens_list returns TRUE or FALSE for whether the input is a valid list-based tokens object.
tif_as_corpus_character takes a valid tif corpus object and returns a character vector corpus object.
tif_as_corpus_df takes a valid tif corpus object and returns a data frame corpus object.
tif_as_tokens_character takes a valid tif tokens object and returns a list-based tokens object.
tif_as_tokens_df takes a valid tif tokens object and returns a list-based tokens object.

The old validate functions have been renamed tif_is_corpus_df, tif_is_dtm and tif_is_tokens_df. This is more in line with base-R functions and separates the "df" version of the corpus and tokens from the alternative new forms.

This is the initial implementation of the ideas discussed at the rOpenSci Text Workshop from 21-22 April 2017.

tif_corpus_validate returns TRUE or FALSE for whether the input is a valid corpus object.
tif_dtm_validate returns TRUE or FALSE for whether the input is a valid document corpus object.
tif_tokens_validate returns TRUE or FALSE for whether the input is a valid tokens object.