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[SOLVED] Computing between data from the same column [message #1068122]

Fri, 12 July 2013 09:41

Paolo Aprile

Messages: 24
Registered: June 2013

Junior Member

Hi!

I'm trying to calculate the difference between 2 numbers listed (consecutively) in the same column.

I have an XML data source and I'm using a computed column to calculate the difference between the value any item and that of the item that follows.

Ideally, given a "value" column, it should be something like:

BirtMath.subtract(row["value",n], row["value",n+1])

This would be very simple if the data where in separate columns but, as it happens, I don't know how to identify the 2 values in the Expression builder to complete the instruction. Is there a definite syntax for this?

Thanks for your attention!

[Updated on: Tue, 23 July 2013 09:31]

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Re: Computing between data from the same column [message #1068273 is a reply to message #1068122]

Fri, 12 July 2013 21:29

Michael Williams

Messages: 1925
Registered: July 2009

Senior Member

One way would be to define a variable in your initialize script or you could probably use a report variable to "", 0, or null or something. Then, in your computed column, you could check the variable against the current row. After you do your calculation, you would set the value of the variable to the current row's value to check against the next row, then write out your computed value to the column. Hope this makes sense. Smile

Let me know if you have questions.

Michael

Developer Evangelist, Silanis

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Re: Computing between data from the same column [message #1072189 is a reply to message #1068273]

Mon, 22 July 2013 09:01

Paolo Aprile

Messages: 24
Registered: June 2013

Junior Member

Hi Micheal! Thanks for your help!
Ok, I finally got around to try your suggestion, and used the following code to initialize my computed column:


if (vars["datavar"] = "")
{
	vars["datavar"] = row["value"];
	"";
}
else if (vars["datavar"] == row["value"])
{
	0;
}
else if (vars["datavar"] != row["value"])
{
	BirtMath.subtract(vars["datavar"], row["value"]);
	vars["datavar"] = row["value"];
}

When I run the report, i get "There are errors evaluating script". Can anyone point out where I went astray? O_o

Thanks for your time!

Paolo

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Re: Computing between data from the same column [message #1072402 is a reply to message #1072189]

Mon, 22 July 2013 17:24

Michael Williams

Messages: 1925
Registered: July 2009

Senior Member

Try something like this:

if (vars["datavar"] == ""){
	vars["datavar"] = row["value"];
	null;
}
else{
	temp = vars["datavar"] - row["value"];
	vars["datavar"] = row["value"];
	temp;
}

Michael

Developer Evangelist, Silanis

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Re: Computing between data from the same column [message #1072689 is a reply to message #1072402]

Tue, 23 July 2013 09:30

Paolo Aprile

Messages: 24
Registered: June 2013

Junior Member

Ok, I customized a little your suggestion and now it works! =)

And not just with numerical data: I was even able to adapt it to calculate the time difference between 2 timestamp in a crosstab!
Thanks for your time and for your help!

Paolo

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