Google line charts how to NOT interpolate missing data

Question

I have a database table with a series of events, these events have dates for when they happen. Now I would like to display the number of events for each month and show them in a line chart. I get the data via php and generate the js-code in a loop using data.addrow

Now this works fine, but if there is a month with no events it will not be added as a row and the line will simply interpolate the missing month. So for example january 5 events, february 0 and march 5 events, would create a horizontal line going from january to march making it look like there where 5 events in february.

How can i make the line go down to zero for a "empty" month?

Do I need to fill in empty rows/months with null? This would not seem very practical.

There are several ways you might have implemented the line chart with date values. Could you provide an example that demonstrates the problem, either in jsfiddle or provide a drawVisualization function that works in the GViz playground: code.google.com/apis/ajax/playground/… — dlaliberte

jmac jmac · Accepted Answer · 2013-04-15T00:41:55

If you want the line to go down to zero, you are interpolating, just in a different way. Google gives you two ways to deal with empty values (nulls) using the interpolateNulls option:

True will guess what value belongs in between (the current behavior in your chart)
False will leave a break in the line for empty data points (not what you want)

To get all null values to show as zero, you would need to go through your data with a for loop and change any null value to 0. Something like the below code.

for (i = 0; i < data.getNumberOfRows(); i++) {
  if ( data.getValue(1, i) == null )
    data.setValue(1, i) = 0
}

The above code isn't tested, and I don't know how your data is set up so I didn't spend much time testing it (I have no idea how many columns, etc. your data has, you can adjust and test as needed).

Google line charts how to NOT interpolate missing data

1 Answers