r - prepare an arules transaction list -

arules requires list of transactions. each row in list contain array of products. not every transaction has same amount of products. sounds pivot it's not. example can found here

i want aggregate(dvd , by=list("id"), fun=c) fail arguments must have same length

this data

> dvd    id          item 1   1   sixth sense 2   1         lotr1 3   1 harry potter1 4   1    green mile 5   1         lotr2 6   2     gladiator 7   2       patriot 8   2    braveheart 9   3         lotr1 10  3         lotr2 11  4     gladiator 12  4       patriot 13  4   sixth sense 14  5     gladiator 15  5       patriot 16  5   sixth sense 17  6     gladiator 18  6       patriot 19  6   sixth sense 20  7 harry potter1 21  7 harry potter2 22  8     gladiator 23  8       patriot 24  9     gladiator 25  9       patriot 26  9   sixth sense 27 10   sixth sense 28 10          lotr 29 10     galdiator 30 10    green mile 

i need list looks

tr1     c("sixth sense","lotr1","harry potter1","green mile","lotr2") tr2     c("gladiator","patriot","braveheart") tr3     c("lotr1","lotr2") .... 

i think split job you.

    df <- structure(list(id = c(1l, 1l, 1l, 1l, 1l, 2l, 2l, 2l, 3l, 3l,  4l, 4l, 4l, 5l, 5l, 5l, 6l, 6l, 6l, 7l, 7l, 8l, 8l, 9l, 9l, 9l,  10l, 10l, 10l, 10l), item = c("   sixth sense", "         lotr1",  " harry potter1", "    green mile", "         lotr2", "     gladiator",  "       patriot", "    braveheart", "         lotr1", "         lotr2",  "     gladiator", "       patriot", "   sixth sense", "     gladiator",  "       patriot", "   sixth sense", "     gladiator", "       patriot",  "   sixth sense", " harry potter1", " harry potter2", "     gladiator",  "       patriot", "     gladiator", "       patriot", "   sixth sense",  "   sixth sense", "          lotr", "     galdiator", "    green mile" )), .names = c("id", "item"), class = "data.frame", row.names = c(na,  -30l))      df <- read.csv(textconnection(txt), header = true, stringsasfactors = false, strip.white = true) result <- split(df$item, df$id) names(result) <- gsub("(.*)", "tr\\1", names(result)) result ## $tr1 ## [1] "sixth sense"   "lotr1"         "harry potter1" "green mile"    "lotr2"         ##  ## $tr2 ## [1] "gladiator"  "patriot"    "braveheart" ##  ## $tr3 ## [1] "lotr1" "lotr2" ##  ## $tr4 ## [1] "gladiator"   "patriot"     "sixth sense" ##  ## $tr5 ## [1] "gladiator"   "patriot"     "sixth sense" ##  ## $tr6 ## [1] "gladiator"   "patriot"     "sixth sense" ##  ## $tr7 ## [1] "harry potter1" "harry potter2" ##  ## $tr8 ## [1] "gladiator" "patriot"   ##  ## $tr9 ## [1] "gladiator"   "patriot"     "sixth sense" ##  ## $tr10 ## [1] "sixth sense" "lotr"        "galdiator"   "green mile"