Unable to add trendlines with only 1 category

[blakebutcher]

Catherine Hanrahan:

The problem I've got is inputting the data. The x and y columns are fine, but with the category column for having two colours (NSW and QLD in the sheet), if I delete these I can't draw a regression line. See this example - http://www.abc.net.au/news/interactives/chart/?chart=boothdata-libsv2000pw. If I leave that column in the sheet, the chart looks like this: http://www.abc.net.au/news/interactives/chart/?chart=boothdata-sa-education-onenation

[blakebutcher]

So http://www.abc.net.au/news/interactives/chart/?chart=boothdata-libsv2000pw does draw a trendline but it is obviously wrong (its draw horizontally across the very top).

I can change the default scatterplot data to just use one category and it seems to work.

I'll try to figure out why the trendline on that specific data is wrong.

[blakebutcher]

TODO: show "Trend line" in legend when there is only 1 category
TODO: hide Legend container when there is nothing to show in there

[blakebutcher]

There is some broken and missing data in http://www.abc.net.au/news/interactives/chart/?chart=boothdata-libsv2000pw that I think is responsible for causing the trendline to be wrong.

[blakebutcher]

I've created #65 to look into adding more data validation to the sheets