affinity analysis using arules "apriori" is giving me zero rules

Question

I am R version 3.4.4 on a Windows 10 machine, and starting with a CSV that looks like this. it has 4247 entries:

  student_id course
1          1  EC402
2          2  EC403
3          3  EC403
4          4  FI201
5          4  LA321
6          4  LA325

I know R won't do much of anything with it in this format. I found this for help: How to prep transaction data into basket for arules

So I applied that to my data frame:

require(arules)
trans <- as(split(df[,"course"],df[,"student_id"],), "transactions")

I go to inspect the transactions, so far, so good. Here's a small snippit:

[14]   {MG900,MK605}                                     14           
[15]   {AC103,EC402,QA811}                               15           
[16]   {EC403,LA301}                                     16           
[17]   {EC408}                                           17           
[18]   {AC111,AC115,LA325,MG503}                         18           
[19]   {EC403}                                           19           
[20]   {QA811}                                           20           
[21]   {MG962}                                           21           
[22]   {AC104,FI201,MG535,MG565}                         22           
[23]   {FI234,FI253,PO000}                               23           
[24]   {EC411}                                           24           
[25]   {CO810,MK611,PO000,SP596}                         25          

But now I want to get some rules of association, and it gives me zero rules.

rules <- apriori(trans, parameter = list(supp = 0.2, conf = 0.8))

The output:

Parameter specification:
 confidence minval smax arem  aval originalSupport maxtime support minlen
        0.8    0.1    1 none FALSE            TRUE       5     0.2      1
 maxlen target   ext
     10  rules FALSE

Algorithmic control:
 filter tree heap memopt load sort verbose
    0.1 TRUE TRUE  FALSE TRUE    2    TRUE

Absolute minimum support count: 329 

set item appearances ...[0 item(s)] done [0.00s].
set transactions ...[153 item(s), 1645 transaction(s)] done [0.00s].
sorting and recoding items ... [0 item(s)] done [0.00s].
creating transaction tree ... done [0.00s].
checking subsets of size 1 done [0.00s].
writing ... [0 rule(s)] done [0.00s].
creating S4 object  ... done [0.00s].

Is there anything I'm doing wrong, or perhaps a different way of doing this? Thanks!