Question : What's an easy way to add cumulatively in Foxpro?

I have a cursor whose data is in the following format:

Date Class Value
1/1/2000 RED 1.5
1/2/2000 RED 1.3
1/3/2000 RED 1.1
1/4/2000 RED 1.7
1/1/2000 BLUE 0.65
1/2/2000 BLUE 0.75
1/3/2000 BLUE 0.85
1/4/2000 BLUE 0.90
1/1/2000 GREEN 21.5
1/2/2000 GREEN 22.5
1/3/2000 GREEN 24.5
1/4/2000 GREEN 23.5

I am trying to add a cumulative value column, which is a sum of the value column, but added from most recent day to past, but done by class, as the following example indicates:

Date Class Value Cum_Value
1/1/2000 RED 1.5 5.6
1/2/2000 RED 1.3 4.1
1/3/2000 RED 1.1 2.8
1/4/2000 RED 1.7 1.7
1/1/2000 BLUE 0.65 3.15
1/2/2000 BLUE 0.75 2.50
1/3/2000 BLUE 0.85 1.75
1/4/2000 BLUE 0.90 0.90
1/1/2000 GREEN 21.5 92.0
1/2/2000 GREEN 22.5 70.5
1/3/2000 GREEN 24.5 48.0
1/4/2000 GREEN 23.5 23.5

What's the easiest and quickest (computationally) way of doing this?

Answer : What's an easy way to add cumulatively in Foxpro?

Several ways exist but the classic xBase code seems to be the most efficient one:

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*-- Suppose the numeric column Cum_Value already exists in YourTable
USE YourTable EXCLUSIVE
INDEX ON Class + DTOC(Date, 1) TAG CompOrder DESCENDING
LOCAL lnCumulSum, lcClass
lcClass = ''
lnCumulSum = 0

SCAN ALL
  
  IF Class == lcClass
    lnCumulSum = lnCumulSum + Value
  ELSE
    lnCumulSum = Value
    lcClass = Class
  ENDIF
  
  REPLACE Cum_Value WITH lnCumulSum
  
ENDSCAN

DELETE TAG CompOrder
GO TOP

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