transform should alert when creating NaN's; and plot should alert when using NaN's

[gweinberg]

Problem

1. Currently when using the tranform tool to make a transformation that creates NaN's (e.g., taking log of a variable that contains zeros), the tool doesn't flag this fact. [This can then, for instance, cause student confusion when attempting to make a plot with a regression line and the line doesn't show up, and it's not clear why.]

2. Following (1), when attempting to make a scatterplot + regression line, with a variable containing NaN's, the line doesn't show up, but the tool doesn't flag the reason why.

Solution

1. When using the transform tool to create a new variable that would contain NaN's (e.g., taking log of a variable containing zeros), when you click "create new variable," it should, for instance, pop up a new dialog, with something like, "The variable you are attempting to create will contain 5 undefined values; do you wish to continue? [Yes][No]."

2. When using scatterplot+regression line with a variable containing NaN's, when it makes the plot, a notification should print somewhere near the plot (maybe below), with something like, "The regression line could not be computed since one or more of the variables had undefined values."

Alternatives

No response

Additional context

None.