When you set a grouping variable (for example you might Barchart Sales grouped by Region) the default is to sum the data into each category defined by the group code. This will give one bar for each unique value in Region, each bar being the total sales for that region. The functions which you can use here are:

• Count,Tally – just report the number of occurrences of that group
• Sum,Total – add up the total value
• Mean,Average – add up the total and divide by the Count
• Minimum – report the lowest value in the group
• Maximum – report the largest value in the group

ch.Set 'head' 'Mean Barley Yield by Year'
ch.Set 'gfn' 'mean'
ch.Set 'gvar' year
ch.Bar yield

All these functions take account of the current Missing Value setting, so totals and averages will correctly omit missing data.

See also ...
GroupBy – group variable
MissingValue – missing value(s)