[Traminer-users] Using the process time axis when converting from SPELL to STS

[Arie Riekhoff]

Hello!

The TraMineR package has been doing a wonderful job with my data and  
it's a real pleasure to work with it, even as a beginner in R. I have  
just run into a problem with the process axis function in the  
seqformat command and I haven't managed to figure out what I'm doing  
wrong.

My data comes in SPELL format and I want to convert it to STS before  
creating a sequence object. Following instruction from the TraMineR  
user's guide this work very nicely if I select process = FALSE.  
However, I need to use the process time axis, because I'm working with  
a cohort of 3 consecutive birth years and I want to start counting  
from the year in which they reach a specific age and then follow them  
for the next 10 years (i.e. 120 months). My data starts in 1999 and  
registers statuses per month. I have recoded the dates, so that  
January 1999 is 1, February 1999 is 2, etc. I want to start the time  
axis for the respondents from the 3 consecutive birth years at t = 1  
(year 1), t = 13 (year 2) and t = 25 (year 3). I have imported a  
separate file with the id's of the respondents and the different start  
times.

So, my command was the following:

> wr.sts.process <- seqformat (wr, id = "ID", begin = "BEGINTIME", end  
> = "ENDTIME", status = SOCECST_rec", from = "SPELL", to = "STS",  
> process = TRUE, pdata = starttime, pvar =c("ID", "start"), limit =  
> 120)
    [>] SPELL data converted into 2088 STS sequences

But it results in missing values (NA) for almost each status.

My wr dataframe with spell data looks something like this:

> wr [1:5,]

     ID    BEGINTIME    ENDTIME    SOCECST_rec
1   1             1         16             1
2   1             17        18             4
3   1             19        20             4
4   1             21        21             4
5   1             22        22             3

I had followed the user guide's advice to convert the status variable  
into an integer.

And my starttime dataframe like this:

> starttime [1:5,]

     ID   start
1    1      13
2    2      13
3    3      25
4    4       1
5    5      25

I also tried converting into converting into a sequence object with  
the seqdef() function directly from spell data, but run into the same  
problem ([!] sequence with index: 1,2,3 etc contains only missing  
values).

Like I wrote, when I use process = FALSE, both seqformat and seqdef  
work perfectly well, so it's not the wr data that's the problem. I  
guess I'm doing something wrong with the process time axis.

Someone might have asked a similar question here before, but I  
couldn't find any definite answers anywhere. I hope that someone can  
point me in the right direction or give me a hint as to the solution  
of my problem!

Thanks in advance,

Aart-Jan