Decide what graph to display when there's no data to graph
While looking through the Rserve logs, I found that we sometimes attempt to graph data that cannot be graphed in a reasonable way. Examples:
- Data from the CSV file ends on 2018-02-13. We try to graph 2018-02-13 to 2018-02-14. A line needs at least 2 points, so we're showing an almost empty graph.
- Data from the CSV file ends on 2018-02-13. We try to graph 2018-02-14 to 2018-02-15. We don't have a single data point to graph, so we're not showing anything at all.
I could imagine we do the following things, if we can't display a single data point or line segment:
- Display a "No Data Available" placeholder like Relay Search.
- Note that we might need this for other cases, too, when users pass parameters that we cannot process.
- We might as well not display anything, which is what we do right now. Might be less usable, though.
- Display an empty graph with all requested dates on the x axis and no data points.
- Note that if we want to do this, we need to decide when to "trim" the graph to the available dates and when to show all requested dates from start to end. Example: Try to draw a graph from 2000-01-01 to 2001-01-01, and then try to draw another graph from 2000-01-01 to 2018-01-01. Should both graphs display the full requested time period, or should just the second graph be trimmed to available data?