
Dear list,
I have the following problem, what i'm trying to do is to built a function which does the following calculationg in a recursive way:


I have a data frame more or less like this:

variable        year         DELTA

EC01             2006            /
EC01             2007           10
EC01             2008            5
EC01             2009            9


And then I have at time 2009  a variable called R_EC01(2009)=5
What I have to do is to construct the R_EC01 time series by starting from the 2009 value:
R_EC01(2008)=R_EC01(2009)-DELTA(2009)
R_EC01(2007)=R_EC01(2008)-DELTA(2008)
R_EC01(2006)=R_EC01(2007)-DELTA(2007)


In terms of number, the results that i should get are:
R_EC01(2008)=5-9=-4

R_EC01(2007)=-4-5=-9
R_EC01(2006)=-9-10=-19
so my data frame should looks like this
SERIES        YEAR             value

R_EC01       2006                  -19

R_EC01        2007                   -9

R_EC01        2008                   -4

R_EC01         2009                   5
Anyone Knows hot to do it??
My dataframe is not set as a time series...


Thanks a lot!!!

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