Add markers to basic plot image

[timhoffm]

Closes #16.

Preview:

[rougier]

If we really want markers over the plot, it should be orange and placed over the sine. Else, it's confusing because it suggests you can to have two different plots with one command.

[timhoffm]

With two datasets I want to stress that plot() can make marker-only plots as well. I consider this important because otherwise people wanting to draw markers only would be guided to scatter(), which is not the right function for plotting simple functional dependencies with markers (c.f. #16 (comment)).

Side note: You can actually draw two plots with one command (either using plot(x, y, x2, y2) or plot(x, y) where y is an 2D array, columns containing the datasets). So it's not wrong if that's insinuated. But it's not my main point and I personally don't think it's the major conclusion people from the suggested image.

[tacaswell]

You can actually draw two plots with one command

I don't think we should highlight that particular feature!

I agree with @rougier here, the rest of the entries are 1:1 of plotting command to the atomic (ish) graphic you get from that element so am 👎 on this change.

I'm 50/50 including a markers on the organge sin and 50/50 on adding another entry to the column,

[tacaswell]

I agree with @rougier that adding a second differently colored dataset is confusing.

[timhoffm]

The overall motivation is to avoid the association: plot is for lines and scatter is for markers, which the current simplification inevitably would promote.

An important question for the styling is the intended direction of the mapping: Does the section list visual plots and annotate them with the needed command? Or does section list our plot commands and the images are illustrations?

Possible solutions:

• Add a second data line to the plot [timhoffm]
  Downside: People have to realize that the picture shows two datasets with different plot variants. IMHO different color and function do help here.
• Draw the single data set with lines and points [rougier, 0.5 * tacaswell]
  Downside: People have to realize that the style can be adapted from lines-and-markers to lines-only and markers-only.
• Add an additional plot [0.5 * tacaswell]
  Downside: There's already very little space.

[jklymak]

I prefer 1, but I suspect rougier doesn't like the second color. I don't see the confusion with the second data set, or having two plot commands in the same section.

[rougier]

I think we should keep it simple since we cannot show everything on cheat sheets. Even the markers on the first plot might be confusing. This of course tends to suggest that for scatter plot you have to use the scatter command, but the cheatsheet might be not the place to explain this is not really the case.

[ghost]

At this time , it will show clearly of plot. I am agree with this code! nice work