R數據表setkey - 錯誤某些列不在data.table中

Question

我想使用帶有預定義列表id和categories data.table setkey ，但是會收到一條錯誤消息：

> setkey(tr_id_cat_dt, id, categories)
Error in setkeyv(x, cols, verbose = verbose) : 
  some columns are not in the data.table: categories

我希望id和categories所有元素都顯示為鍵。

這可能嗎？

---

id和categorie是值列表，例如：

categories = c(9115L, 9909L, 3203L, 5558L, 4401L, 1703L, 1726L, 3504L, 3509L, 
5122L, 5616L, 5619L, 2202L, 2119L, 6202L, 5824L, 799L, 4517L, 
7205L, 706L)


dput(head(tr_id_cat_dt))
structure(list(id = c(86246, 86246, 86246, 86246, 86246, 86246
    ), category = c(706L, 706L, 706L, 706L, 706L, 706L)), .Names = c("id", 
    "category"), sorted = c("id", "category"), class = c("data.table", 
    "data.frame"), row.names = c(NA, -6L), .internal.selfref = <pointer: 0x015424a0>)

Answer 1

您只能在setkey的列上設置data.table （正如@Roland已經指出的那樣）。

require(data.table)
DT = data.table(x = 1:2, y=3:4)
z = 5:6
setkey(DT, x) # works
setkey(DT, z) # doesn't
# Error in setkeyv(x, cols, verbose = verbose, physical = physical) : 
#   some columns are not in the data.table: z

setkey(DT[, z := z], z) # works

HTH