R: Using decompose() in data.table - r

Question

Hi I have a time series data as follows:
Code Year Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
1001 2009 183 175 151 173 169 169 158 132 91 91 146 114
1001 2010 76 103 130 103 78 72 64 96 89 91 61 62
1001 2011 73 50 99 90 74 112 113 111 112 112 97 137
1001 2012 105 140 160 129 162 161 150 167 151 161 114 120
1001 2013 140 137 153 128 137 137 135 148 116 134 121 95
1001 2014 135 145 144 110 109 130 110 58 100 109 67 66
1015 2009 21 19 19 21 17 29 56 35 46 33 42 45
1015 2010 46 29 55 62 49 48 44 37 39 46 33 39
1015 2011 59 36 52 41 36 38 42 43 37 37 37 35
1015 2012 46 53 55 41 69 41 38 42 37 50 46 48
1015 2013 64 43 58 43 50 39 29 48 45 26 51 55
1015 2014 40 54 64 58 76 59 69 66 57 60 58 55
1031 2009 2408 2370 2799 3460 3263 3102 2769 2749 3018 3283 3343 3193
1031 2010 3130 3069 3776 3348 3341 4129 3920 4131 4152 4044 4241 3522
1031 2011 3454 3768 5217 4242 4624 5105 4712 6064 5546 6049 5957 4670
1031 2012 4959 3554 2163 1274 1452 1248 1303 1278 916 906 522 324
1031 2013 537 442 417 389 469 423 328 246 291 387 201 122
1031 2014 249 203 42 30 29 36 39 16 36 23 11 19
I am trying to find the decomposition of the timeseries by Code column as different Codes have different trends and seasonality during various months.
I tried using data.table but it gives me error. Following is the code that I am using:
sa_data_ssn_cnt_ts <- data.table(sa_data_ssn_cnt_ts)
sa_data_ssn_cnt_si <- sa_data_ssn_cnt_ts[,list(SI = decompose(sa_data_ssn_cnt_ts, type = "multiplicative", filter = NULL)), by = sa_data_ssn_cnt_ts$site_id]
Error that I get:
Error in decompose(sa_data_ssn_cnt_ts, type = "multiplicative", filter = NULL) : time series has no or less than 2 periods
What is it that I am messing up here?
Is there any other way that I can get the decompositions by Code column?
Thanks a lot for the help.