Displaying Groupby data with Google Charts

Question

I want to use Google charts(stack bar) to visualize the data, which has two string fields and one number field.
Data->[string,string,number]
When I try to implement the same I am getting following error
"All series on a given axis must be of the same data type"

Answer 1

check the data format for a BarChart

only the first column may be a 'string'