extjs group by letter

does anyone knows how to use extjs's groupingview and group by the first开发者_JS百科 letter of the particular field indicated by the groupingStore?

For instance:

group 'l':
record with field 'lion'
record with field 'leopard'

group 'g':
record with field 'giraffe'

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ok i got it. Basically I need to edit the grid column's groupRenderer :

groupRenderer:function(v,u,r,rowIndex,colIndex,js){
            return r.get('fieldname').charAt(0);
        },