Error in levels for seqdef in R

Question

I've seen this error everytime I try to run seqdef on my data that has already been converted to STS format using seqformat. A sample of my dataframe looks like

head(df.new, 10)
   user_id orderdate         cart to
1        8         1      produce 30
2        8        31      produce 60
3        8        61      produce 70
4        8        71      produce 92
5       10         1      produce 30
6       10        31      produce 42
7       10        43 meat seafood 56
8       10        57         deli 77
9       17         1    beverages  3
10      17         4    beverages  8

It has a total of 14000 rows of orders and there are some orders which occur on the same day for each user (i.e. orderdate == to). Below are the codes that I have used to create my STS data which is used as input to seqdef.

df.form <- seqformat(df.new, id='user_id', begin='orderdate', end='to', status='cart', from='SPELL', to='STS', process=FALSE)
df.seq <- seqdef(df.form, left='DEL', right = 'unknown', xtstep=10, void = 'unknown')

The error message I get when running the seqdef is

 [>] found missing values ('NA') in sequence data
 [>] preparing 35000 sequences
 [>] coding void elements with 'unknown' and missing values with '*'
 [>] 21 distinct states appear in the data: 
     1 = alcohol
     2 = babies
     3 = bakery
     4 = beverages
     5 = breakfast
     6 = bulk
     7 = canned goods
     8 = dairy eggs
     9 = deli
     10 = dry goods pasta
     11 = frozen
     12 = household
      ...
 [>] adding special state(s) to the alphabet: unknown
Error in `levels<-`(`*tmp*`, value = if (nl == nL) as.character(labels) else paste0(labels,  : 
  factor level [24] is duplicated

I tried removing those orders where orderdate == to and the same error still occurs. I would appreciate any help I can get to fix this problem. Thanks.

Answer 1

The error occurs because you are using the same code ('unknown') for right missings and voids.

When the sequences contain 'missings', these missings will be considered as a separate state when you set with.missing = TRUE in functions such as seqdist or seqdplot, while voids are used to adjust the row lengths and are simply ignored when plotting the sequences (seqplot) or computing dissimilarities (seqdist).