R help - Mar 2009 - Creating variables with different levels depending on conditions

Dear R-help-list, 

I started using R coming from the former use of SPSS, mainly writing my own
syntax. 
I do classical experimental cognitive psychology and am interested in the
cognitive control of task sequences (i.e. classification task). Especially I
am interested in the performance of the actual depending on the tasks
before. Thus, in SPSS I create variables like this one: 

Compute cond = 0. 
If (task_2=task) cond=1 else cond=2. 

task refers to the actual task and task_2 to the task performed 2 trials
before, cond=0 is used later to filter off the first two tasks in every
block. 

So far, I could create all variables I need in R like in SPSS. However, I
don't succeed creating a variable like "cond (=condition)" in R. I
managed
to create a variable that is either true or false, but I would prefer a
categorical variable to get a table which I can use later for t-test and
anovas. I am bit puzzled that this simple syntax in SPSS has no equivalent
in R or am I just to blind to find it? All suggestions are cordially
welcome, miriam 



Dr. Miriam Gade
University of Zuerich
Institute of Psychology, General Psychology (Cognition)
Binzmuehlestr. 14, Box 22
CH-8050 Zuerich
Phone: +41 (0)44 6357-461

Miriam Gade wrote:
> Dear R-help-list, 
>
> I started using R coming from the former use of SPSS, mainly writing my own
> syntax. 
> I do classical experimental cognitive psychology and am interested in the
> cognitive control of task sequences (i.e. classification task). Especially
I
> am interested in the performance of the actual depending on the tasks
> before. Thus, in SPSS I create variables like this one: 
>
> Compute cond = 0. 
> If (task_2=task) cond=1 else cond=2. 
>
> task refers to the actual task and task_2 to the task performed 2 trials
> before, cond=0 is used later to filter off the first two tasks in every
> block. 
>
> So far, I could create all variables I need in R like in SPSS. However, I
> don't succeed creating a variable like "cond (=condition)" in
R. I managed
> to create a variable that is either true or false, but I would prefer a
> categorical variable to get a table which I can use later for t-test and
> anovas. I am bit puzzled that this simple syntax in SPSS has no equivalent
> in R or am I just to blind to find it? All suggestions are cordially
> welcome, miriam 
>
>   
Hi Miriam,
Try this:

cond<-0
cond<-ifelse(task_2 == task,1,2)

and you can probably do all the values at once by vectorizing this.

Jim