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TOPIC: Expression Manager: Nested Equations?

Expression Manager: Nested Equations? 1 year 6 months ago #90492

  • Fred
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Can you use the result of equation question A in equation question B on the same page and have it computed and displayed correctly?

I am trying this and the first equation looks ok, but the second one doesn't seem to pick up the result of the first.

For example, assume a group-by-group survey, with the following group:

Q1 (numeric) Apples? Response: 6
Q2 (numeric) Bananas? Response: 3
Q3 (equation) Subtotal fruit. Expression {Q1+Q2}. Displays 9.
Q4 (numeric) Carrots? Response: 2
Q5 (equation) Fruit minus Veggies. Expression {Q3 - Q4}. Should display 7, but is showing -2.

I am using 1.92+ (the final build)
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Re: Expression Manager: Nested Equations? 1 year 6 months ago #90496

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It should work. Please upload a sample survey or group demonstrating the problem.
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Re: Expression Manager: Nested Equations? 1 year 6 months ago #90503

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Hi Tom,

I probably should have titled the topic "Cascading Equations." The actual survey is REALLY long, but here's a short one demonstrating the problem.

The equations work correctly with small numbers. but starts to fail when the numbers get bigger (q3 >=1000)

Looking at this some more, it seems like has to do with using number_format() on the equations, which I didn't mention originally. The original survey (the long one) is mostly financial/money questions and I wanted to display the equations rounded and with comma-separators.

So when q3 gets to 1000, then the number_format inserts the comma and the 2nd equation is looking at the first one and saying "That's not a number"?

Do you think that is the problem? If so, is there some way to re-cast the string as a number? I tried changing q5 to {number_format(intval(q3) - q4)}, but that didn't help.
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Re: Expression Manager: Nested Equations? 1 year 6 months ago #90505

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Here's the survey...
Attachments:
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Re: Expression Manager: Nested Equations? 1 year 6 months ago #90506

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The other problem with the number_format() is that is will save to the DB as a string. For example, 100000 is saved as 100,000. Just as it is displayed. It will create some problems down the line when we export the data for analysis.

What I need to do is display numbers with comma-separators and rounding, but have the value stay a number and be saved that way.
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Re: Expression Manager: Nested Equations? 1 year 6 months ago #90507

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I recommend storing numbers instead of formatted strings via your equations. You can use number formatting options to have those valuea dispay with formating. I will take a look at the actual survey tomorrow.
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Re: Expression Manager: Nested Equations? 1 year 6 months ago #90509

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Awesome, thanks Tom.

We use javascript masking on the numeric inputs to get the #,### format. When people are entering numbers in the millions, it's easy to make mistakes without them. Unfortunately you can't use masking on Equations as far as I can tell.

I also considered as an alternative trying to replace the Equation with a Numeric question and put the expression in the Default value. However, the Default expression doesn't update in real time when the inputs are on the same page; you have to put it on a following page, and we need it on the same page.
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Re: Expression Manager: Nested Equations? 1 year 6 months ago #90514

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Fred-

Try this version of your survey.


File Attachment:

File Name: limesurvey_survey_383381.lss
File Size: 31 KB



I always use equations as hidden calculations, then display the resulting values in a different question. That way you can store pure numbers that are easy to manipulate and analyze, but you can display them however you want.

As you can see from this demo, cascaded Equations work just fine on the same page.

Here is a screen shot.


cascaded-equations.jpg



-Tom
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Re: Expression Manager: Nested Equations? 1 year 6 months ago #90516

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Now why didn't I think of that? :). Will try it out today.

This survey actually has over 500 of these equations, and now we are doubling the number of questions. Although the display questions don't create a column in the survey_NNN table at least. It's a good thing I am using Excel and your awesome Excel importer to create all the questions.

Maybe in a future version all this masking and formatting will be baked in and a lot easier to use.
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Re: Expression Manager: Nested Equations? 1 year 6 months ago #90519

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Works great. Thanks Tom.
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