Introduction vignette

[teunbrand]

This PR attempts to fix #4620.

Briefly, it adds a vignette that attempts to introduce new people to the essentials of ggplot2 in less than 1000 words.

I'm not an avid writer, so I'd welcome any feedback, including but not limited to spelling fixes, suggestions for phrases, structural comments, rmarkdown faux-pas corrections, general tips etc.

Also, I took @thomasp85's idea for a graphic to help introducing ggplot2.

[thomasp85]

@mine-cetinkaya-rundel if you have time to read this through with the eyes of an educator I'd be grateful. If not that is totally fine

[mine-cetinkaya-rundel]

Thanks for contributing this vignette, I can see the value in an introductory vignette in a package. However, I do think a few non-trivial updates would make this vignette much stronger and much more useful to the new learner.

1. Start with the final graphic and break it down: This is the approach we use in R4DS (https://r4ds.hadley.nz/data-visualize.html#sec-ultimate-goal) and generally my teaching philosophy (cake first!). This gives a direction and purpose from the beginning and then learners are exposed to the pieces that build up to that goal.
2. Avoid filler words and use accurate terms instead: I've commented in a few places in the vignette about words like "thing", "something", etc. I think an introductory vignette is a great place to expose learners to the terminology that will help them not just learn but also articulate their questions better.
3. Highlight an example that makes all layers sensible: My suggestion in the review comments is cty and hwy as variables so that coord_fixed() can be sensible, for example.

The main question that @thomasp85 will want to answer though is whether a vignette that replicates the approach of introductory materials from elsewhere (in this case R4DS) is a useful addition or if it's sufficient to link to those resources from the package docs. I can see the value in both ways. If the goal is to include this vignette, I'd be happy to review the revised version.

[mine-cetinkaya-rundel]

"understood by the graphics system" sounds vague/odd, I think it's more about how the graphics system will use/visualize the data.

[teunbrand]

For the last sentence here, does the analogy 'It is the 'dictionary' to translate tidy data to the graphics system.' work well enough?

[teunbrand]

Thanks for the review, Mine, these comments all contain pieces of wisdom I hadn't yet considered!

My personal thoughts are that this vignette should very tersely show all layers of the grammar involved and serve as advertisement to the ggplot2 book where the information is a lot richer. I'll await Thomas' judgement what, and whether, this vignette should be.

[thomasp85]

let's go with adding this as a "getting started" vignette (i.e. rename the vignette to ggplot2.rmd) and incorporate the suggestions Mine made

[teunbrand]

I think this ready for further review

[mine-cetinkaya-rundel]

The revised version looks great. I made a series of comments that I recommend incorporating before merging.

[teunbrand]

Thank you so much @mine-cetinkaya-rundel for reviewing all this, you have a sharp eye for this. I've incorporated your latest suggestions. I didn't add alt-text to some places where you mentioned it was missing, mostly because the plot was hidden in the chunk options.

[thomasp85]

LGTM

[yutannihilation]

Thanks for this great introduction vignette!