Sum of Year and Previous Year in Script - Skip last Year

[#1]

I wanna calculate the Sum of the Sales for one year and the previous for different companies.

However, I do not want a value for 2010 as there is no value to be calculated.

Currently it sums up for example

A, 2015, 100

+

B, 2010, 100

as it seems to go row by row. How can I fix this?

z:

load * inline [

Company, Year, Sales

A, 2010, 100

A, 2011, 110

A, 2012, 120

A, 2013, 130

A, 2014, 140

A, 2015, 100

B, 2010, 100

B, 2011, 110

B, 2012, 120

B, 2013, 130

B, 2014, 140

B, 2015, 100

C, 2010, 100

C, 2011, 110

C, 2012, 120

C, 2013, 130

C, 2014, 140

C, 2015, 100

];

zz:

load Year,

Sales + Previous(Sales) as TwoYearSales

Resident z;

[susovan]

Hi,

Is it your requirement?