# Calculate age in an Equation type question, using Date of Birth

4 years 9 months ago #84934 by TMSWhite
TMSWhite replied the topic: Calculate age in an Equation type question, using Date of Birth
Date math is such a common need that we really ought to add date-related functions to Expression Manager, such as day(), month(), year(), age(date_of_birth [, today]), etc.

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4 years 9 months ago #85032 by tpartner
tpartner replied the topic: Calculate age in an Equation type question, using Date of Birth
tfj, I don't have IE8 here to test but try changing:
`var age = (today_year) - birth_year;`

To:
`var age = Number(today_year - birth_year);`

Cheers,
Tony Partner
Solutions, code and workarounds presented in these forums are given without any warranty, implied or otherwise.

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4 years 9 months ago #85033 by tpartner
tpartner replied the topic: Calculate age in an Equation type question, using Date of Birth

Date math is such a common need that we really ought to add date-related functions to Expression Manager...

Great idea Tom.

Cheers,
Tony Partner
Solutions, code and workarounds presented in these forums are given without any warranty, implied or otherwise.

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4 years 9 months ago #85043 by tfj
tfj replied the topic: Calculate age in an Equation type question, using Date of Birth
I changed the line to:

var age = Number(today_year - birth_year);

The calculation still places a "19" to the front of the age in Internet Explorer 8 (for dates of birth prior to 2000), but not in Internet Explorer 9 or Firefox 14. For example, the age may be calculated as 1929 instead of 29. For the years 2000 and later, the age is calculated correctly.

For now, in order to meet my deadline, I added the two questions (Date of birth and age) in one of our surveys, but hid the age question and commented out the code. That way, in case a script fix comes up, I can put it in without deactivating the survey. I am still calculating the age after-the-fact with a MySQL script.

Thanks, all!

tfj

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4 years 9 months ago #85210 by tfj
tfj replied the topic: Calculate age in an Equation type question, using Date of Birth
I believe I found a solution, after much digging in PHP reference manuals, web searches, etc. I am now able to perform date calculations using the Expression Manager. I modified an example given in PHP and MySQL Web Development, Fourth Edition, by Welling and Thomson (pp. 477-478) (to give proper credit).

Here's what I did:

1) Created a Date of Birth question, of type "Date." The question code I used was "DateofBirth," which you will see in step #2 below. For our purposes, all dates are mm-dd-yyyy.

2) In a separate group that follows the Date of Birth question, I made up an Equation type question, with the following in the "Question" box:

{floor((time() - mktime(0,0,0,substr(DateofBirth,5,2),substr(DateofBirth,8,2),substr(DateofBirth,0,4)))/(365.25*24*60*60))}

This question may be hidden, depending upon your particular needs.

If you need to calculate days, then take out the "365.25" in the script, and so on.

So far in my testing, this seems to be working, but someone may find an improvement, etc. If so, I would appreciate your sharing it.

One other note: the more I use the new Expression Manager, the more I appreciate it.

tfj

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4 years 9 months ago #85320 by Ben_V
Ben_V replied the topic: Calculate age in an Equation type question, using Date of Birth
Very nice solution...
Maybe the improvment could be to get it working with the 2 questions in a same group

I attach the sample survey I've created to make a try.

Thank you to share...
Ben/

Benoît

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Demo Surveys => goo.gl/HuR6Xe (already included in /docs/demosurveys)
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4 years 5 months ago #91050
PawsInMotion replied the topic: Calculate age in an Equation type question, using Date of Birth
These have all been incredibly helpful! Thank you!

Here's a trick I'm trying to figure out though (without knowing perl or much scripting at all):

How do I show year and month (and, optionally, days) from birth as chosen in the previous question.
Some of my clients aren't a year old yet (dogs) or are a year and some months.

I appreciate the help. I'll keep noodling with this code. At least I figured out that 'floor' means to round the answer.

{floor((time() - mktime(0,0,0,substr(DateofBirth,5,2),substr(DateofBirth,8,2),substr(DateofBirth,0,4)))/(365.25*24*60*60))}

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4 years 5 months ago #91155 by tfj
tfj replied the topic: Calculate age in an Equation type question, using Date of Birth
PawsInMotion:

The code I used is modular in the sense that you can substitute values in it to come up with whatever type of date measurement you need.

For instance, instead of using the following for years:

{floor((time() - mktime(0,0,0,substr(DateofBirth,5,2),substr(DateofBirth,8,2),substr(DateofBirth,0,4)))/(365.25*24*60*60))}

you can change it to:

{floor((time() - mktime(0,0,0,substr(DateofBirth,5,2),substr(DateofBirth,8,2),substr(DateofBirth,0,4)))/(24*60*60))}

for the number of days. From there, you could use Equation-type questions to come up with months and days, etc.

I tested this on a couple of cases and they seemed okay. Please let me know if your experience is different.

tfj

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3 years 11 months ago #97877 by DWS
DWS replied the topic: Calculate age in an Equation type question, using Date of Birth
the example works fine... but if yo hide the question then you can't use the value on following questions

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