user defined function issue

[#1]

Hey all,

first off all I am quite new to the QlikView Community and still only have a basic knowledge in the use of QlikView. I am reading temperature and humidity data from a database. I can show all the values in diagramms and so on, no problem. But now I want to create a user defined function to calculate the total amount of water in the air. Therefore I have a formular:

0.622 * (rel. hum * saturated vapour pressure) / (air pressure - rel. hum * saturated vapour pressure)

To test the function I use a fix value for saturated vapour pressure at 20°C = 2337

I built following function in QlikView:

0.622 & '*' & (Only({$} $1) & '*' & 2337) & '/' & (101300 & '-' & Only({$} $1) & '*' & 2337)

Now I want to use this function in a diagramm, so that for every value of a dimension the function Only() picks its value. But it doesn't work How can i fix this? I would be very happy about any help! Thanks a lot.

BR

Henrik

[MarcoWedel]

please post sample data/app

[Peter_Cammaert]

How and where do you call your user-defined function?

[Colin-Albert]

Only(fieldname)  will return a value if the field has just one selected value. If the field has more than one value selected then only(fieldname) will return null.

Thus your expression will return null unless every field value is filtered to only select a single value  - not what you want.

You should be able to use  a similar expression to

     0.622 * (rel. hum * saturated vapour pressure) / (air pressure - rel. hum * saturated vapour pressure)

directly in the chart.

Simply substitute each item such as "rel. hum", "saturated vapour pressure" etc, with the field names that hold the data.

You do not need to create a user defined function, just create an expression in your chart.

Can you post some example data?

[MarcoWedel]

Hi,

one possible solution could be:

SET vRel2AbsHum = 0.622*$1*2337/(101300-$1*2337);

tabHumidity:
LOAD Dual(RecNo()&' RH%', RecNo()) as rel.hum
AutoGenerate 100;

hope this helps

regards

Marco

[#6]

it's an expression that takes parameters and parameters are identified by their position using $1, $2 etc.

check Marco reply.

Jagan uses it in this thread.

Calculating Months difference between two dates

[#7 · Accepted solution]

IN LOAD SCRIPT WRITE:

SET YourFomulaName= Num(0.622 * ( $1  *  $2 )   / (($3-  $1)  * $2));

Let's say your dimension's name is RELHUM

then in the expression

=$(YourFormulaName(RELHUM,2337,101300))

Note: no need for {$} as it implies the current selection by default.

check this thread

Calculating Months difference between two dates

[#8]

Try chaining it:

saturated vapour pressure

=$(YourFormulaName(RELHUM,=$(VapPress(Temp)),101300))

[#9]

Hey,

first of all I would like to thank you for all the responses. I reviewd the different methods to achieve my goal. Finally I used this function and it worked as I wanted:

SET udf_water_content = Num(0.622*($1*$2)/(($3-$1*$2)));

But now I sure want to get the saturated vapour pressure of the measured temperature.

water_content = $(udf_water_content(humidity,=$(VapPress(=$(round(temperature))),101300));

I have a table with temperatures from -20 to 99 °C with the associated saturated vapour pressures. So how can I define the VapPress function to select the vapour pressure of the associated temperature? Attached you can see the table with the preassures. And not to forget: The meassured temperatures are floats, so I would need ro round them.

Thanks for all following replys.

BR

Henrik

[MarcoWedel]

Hi,

please close this thread by selecting an answer that solved your problem and open another thread for your new question.

Thanks

Regards

Marco