Sum operator

[Andee Rubin]

I tried to add up a bunch of variables across a row using the SUM() operator and got strange results.  I listed the variables to be added inside the SUM parentheses separated by commas.  Is that not the right format?  If I use standard infix notation (V1+ V2 + V3), I get the expected results.  I can provide the file if it’s obvious to you what’s going on.

[Andee Rubin]

Sorry – I mean I can supply the file if it’s NOT immediately obvious to you what’s going on!

[Bill Finzer]

Hi Andee,

The sum function expects a single expression to be summed over all cases. Here’s the documentation:

sum(number, filter)

Returns the sum of its argument evaluated for every case.

sum(grade_point) computes the sum of the grade points sum(Mass, Height>60) returns the sum of the masses for heights taller than 60

The strange results you get from sum(V1,V2,V3) are the result of summing the values of V1 over all cases for which V2 look true, totally ignoring V3.

V1+V2+V3 is the best way to get the sum of the values for the three attributes for each case.

Hope this helps,

Bill

[Andee Rubin]

Totally helps!  I will not use that function again for these purposes!

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