Using variables in master items

[mkanaa123]

hi all i have around 100 master items measures  are there ,

For each expression  in master item  , i am writing the expression as

Expression1:

Sum(IF(XNum= 1,Field1,
if(XNum=2,Field1/SomeField1,
if(XNum=3,Field1-SomeField1))))

Expression2:

Sum(IF(XNum= 1,Field2,
if(XNum=2,Field2/SomeField1,
if(XNum=3,Field2-SomeField1))))

Now i want to automate this expression using one variable for XNum

And use that variable in master item expression .

Can anyone please help me

Going forward i want to add one more XNum=4 and Xnum=5  No need of going everywhere and change the expression everytime in each expression for each masteritem,

Can anyone please help me

I dont want in backend script , 

I need in front end variable .

[mkanaa123]

anyoneplease help

[Channa]

load * inline [NUM

1

2

3....]

create variable vNum =NUM

Sum(IF(XNum= 1,Field2,
if(XNum=2,Field2/SomeField1,
if(XNum=3,Field2-SomeField1))))

change expression as below

Sum(IF(XNum= $(vNum),Field$(vNum),
if(XNum=Field$(vNum),Field$(vNum)/SomeField1,
if(XNum=Field$(vNum),Field$(vNum)-SomeField1))))

this is just same will help to change field based on filter selection

use filter as NUM column which is inline load

[AustinSpivey]

I think you're needing dollar-sign expansion with parameters. Here's a Qlik Help article about it. In your case, you can create a new variable that will act like a custom function:

Sum(If(XNum=1, $1,if(XNum=2, $1 / SomeField1,if(XNum=3, $1 - SomeField1))))

Then you can use the new function like this, by simply using the desired fieldname as a parameter in the new variable:

You'll then only need to update the MyFunc variable in the future.