How to create a variable which varies depending on another variable

[Ella Ki]

Hi,

I want to generate a variable which would be equal to y if variable x were bigger than n or equal to z if x were smaller than or equal to n.

For example, if age>50, I would like "experience"=age+10, but if age<=50 then I would like "experience"=age*5.

Is something like this possible?

Thanks.

[Joseph Coveney]

help cond()

Example:

generate double experience = cond(age <= 50, 5 * age, age + 10)

[Ella Ki]

Thanks a lot!

[Ella Ki]

help cond()

Example:

generate double experience = cond(age <= 50, 5 * age, age + 10)

Is it possible to do this:

generate a new variable with the following conditions:

If eyear>1991 and syear<1991, newvariable= totexp - (eyear - 1991)

If eyear>1991 and syear>1991, newvariable= totexp + (syear - 1991)

If eyear <1991, newvariable = difference

Where eyear, syear, totexp and difference are all existing variables?

[Joseph Coveney]

Is it possible to do this:

generate a new variable with the following conditions:

If eyear>1991 and syear<1991, newvariable= totexp - (eyear - 1991)

If eyear>1991 and syear>1991, newvariable= totexp + (syear - 1991)

If eyear <1991, newvariable = difference

Where eyear, syear, totexp and difference are all existing variables?

Yes. You can nest the function.

generate double new_variable = cond(eyear < 1991, difference, cond(syear < 1991, totexp - eyear - 1991, totexp + syear - 1991))
replace new_variable = . if eyear == 1991 | syear == 1991

[Clyde Schechter]

It is certainly possible to nest calls to -cond()- as shown by Joseph. But the resulting code is difficult to look at and understand. I think -cond()- works fine for a simple two-way calculation: do this in one circumstance and do that otherwise. But where you have 3 or more branches, I think it is better to write things out more clearly as:

gen newvariable = totexp - (eyear-1991) if eyear > 1991 & syear < 1991
replace newvariable = totexp + (syear - 1991) if eyear > 1991 & syear > 1991
replace newvariable = difference if eyear < 1991

If you come back to this code in a few months (or even a few days) you can look at it and understand at a glance what it does. If you use nested -cond()- you will probably struggle to grasp it.

By the way, completely as an aside, your criteria do not cover the possibility that eyear == 1991. Is it supposed to be that way, or is that an error?

[Ella Ki]

It is certainly possible to nest calls to -cond()- as shown by Joseph. But the resulting code is difficult to look at and understand. I think -cond()- works fine for a simple two-way calculation: do this in one circumstance and do that otherwise. But where you have 3 or more branches, I think it is better to write things out more clearly as:

gen newvariable = totexp - (eyear-1991) if eyear > 1991 & syear < 1991
replace newvariable = totexp + (syear - 1991) if eyear > 1991 & syear > 1991
replace newvariable = difference if eyear < 1991

If you come back to this code in a few months (or even a few days) you can look at it and understand at a glance what it does. If you use nested -cond()- you will probably struggle to grasp it.

By the way, completely as an aside, your criteria do not cover the possibility that eyear == 1991. Is it supposed to be that way, or is that an error?

Yes you are right, I think I meant to write <= in the last one.

Thanks everyone!