Fix typo in definition of tidy data in README

[mfgeary]

The README (README.md and README.Rmd) files have a typo in the definition of tidy data. I changed the text from "Every column is variable" to "Every column is a variable".

It's a very minor change but important because these sentences have different meanings. Without the "a", it is more difficult to understand what tidy data is, and this is the first thing you see when you go to tidyr's homepage.

[matthewjnield]

@mfgeary Good catch!

I'm adding an idea here for the maintainers' consideration:

Should the definition of tidy data in the tidyr README and website be updated to match the one that is presented in "R for Data Science (2e)", or perhaps vice-versa? The two definitions are very close, and I think they get the same point across, but tidy data is a core concept in the tidyverse, and having a uniform definition (whichever of these two makes the concept clearer) in these two places may be a good idea.

[hadley]

Thanks @mfgeary!

@matthewjnield isn't it the same definition?

[matthewjnield]

@hadley they are very close; I am only wondering if the extra wording in R for Data Science 2(e) gets the point across slightly better and should be added to the tidyr README.

Here are the parts from each source I am referring to:

R for Data Science 2(e):

1. Each variable is a column; each column is a variable.
2. Each observation is a row; each row is an observation.
3. Each value is a cell; each cell is a single value.

tidyr README:

1. Every column is a variable.
2. Every row is an observation.
3. Every cell is a single value.

[hadley]

Oh I see. Do you want to do a PR?

[mfgeary]

@matthewjnield @hadley I chose the shorter definition to be consistent across tidyr as it is also used in the tidy data vignette here. If we switch to the definition from R4DS, I suggest switching all definitions of tidy data in tidyr to be consistent

[matthewjnield]

@hadley Certainly; could you please take a look at #1530 to determine whether that change will be merged or not, before I add another pull request affecting the README for this? That way I can keep the unrelated changes in separate PRs, and keep them coming from a single branch to avoid conflicts in case the first change isn't merged.

@mfgeary Thanks for pointing out the appearance of the definition in the vignette.

[matthewjnield]

This is ready, in #1532.