Question

我正在尝试从2列和数据表的任意行数创建向量列表。与我正在使用的类似的示例数据表是：

dt <- data.table(a = c(1,2,3,4,4,4,3,5,7), 
                 b=c(12,13,14,15,15,16,17,22,18),
                 c=c(1,1,1,1,2,1,1,1,1),
                 d=c("cat1", "cat2", "cat1", "cat1", "cat2", "cat3", "cat2", "cat1", "cat2"))


   a  b  c   d
 1: 1 12 1 cat1
 2: 2 13 1 cat2
 3: 3 14 1 cat1
 4: 4 15 1 cat1
 5: 4 15 2 cat2
 6: 4 16 1 cat3
 7: 3 17 1 cat2
 8: 5 22 1 cat1
 9: 7 18 1 cat2

我想使用by语句对行进行分组，然后使用函数创建列表。但是，我无法让一切工作。这就是我所拥有的：

create_kv <- function(x,y) {
  l <- list()
  i <- 1
  while (i <= length(x) & i <= length(y)) {
    each_c <- c(x[i], y[i])

    l[[i]] <- each_c
    i = i + 1
  }
  return(l)
}

for (each_a in unique(dt$a)) {
    for (each_b in dt[a == each_a,]$b) {
       ranks <- dt[a == each_a & b == each_b,]$c
       inv <- dt[a == each_a & b == each_b,]$d
       dt[a == each_a & b == each_b, `:=` (inv_flow = create_kv(ranks, inv))]
   }
}

不幸的是，即使我使用b="a,b"，循环也无法正确组合行。相反，我得到了：

    a  b c    d   inv_flow
 1: 1 12 1 cat1  1,cat1
 2: 2 13 1 cat2  1,cat2
 3: 3 14 1 cat1  1,cat1
 4: 4 15 1 cat1  1,cat1
 5: 4 15 2 cat2  2,cat2
 6: 4 16 1 cat3  1,cat3
 7: 3 17 1 cat2  1,cat2
 8: 5 22 1 cat1  1,cat1
 9: 7 18 1 cat2  1,cat1

我所希望的是：

    a  b c    d   inv_flow
 1: 1 12 1 cat1  1,cat1
 2: 2 13 1 cat2  1,cat2
 3: 3 14 1 cat1  1,cat1
 4: 4 15 1 cat1  c(1,cat1), c(2,cat2)
 5: 4 16 1 cat3  1,cat3
 7: 3 17 1 cat2  1,cat2
 8: 5 22 1 cat1  1,cat1
 9: 7 18 1 cat2  1,cat1

每个a,b对都有一行。

Answer 1

这是你需要的吗？

dt <- dt[ , inv_flow := paste(c, d, sep=",")][, list(inv_flow = if (.N > 1) list(c(paste0("c(",inv_flow,")"))) else list(c(inv_flow))), by = "a,b"]

#   a  b            inv_flow
#1: 1 12              1,cat1
#2: 2 13              1,cat2
#3: 3 14              1,cat1
#4: 4 15 c(1,cat1),c(2,cat2)
#5: 4 16              1,cat3
#6: 3 17              1,cat2
#7: 5 22              1,cat1
#8: 7 18              1,cat2

str(dt)
# Classes ‘data.table’ and 'data.frame':  8 obs. of  3 variables:
# $ a       : num  1 2 3 4 4 3 5 7
# $ b       : num  12 13 14 15 16 17 22 18
# $ inv_flow:List of 8
# ..$ : chr "1,cat1"
# ..$ : chr "1,cat2"
# ..$ : chr "1,cat1"
# ..$ : chr  "c(1,cat1)" "c(2,cat2)"
# ..$ : chr "1,cat3"
# ..$ : chr "1,cat2"
# ..$ : chr "1,cat1"
# ..$ : chr "1,cat2"
# - attr(*, ".internal.selfref")=<externalptr>

Answer 2

由于它是一个小型数据集，您可以将数据重新整形为data.frame并使用plyr对其进行汇总。不是一个完整的解决方案，但应该让你开始：

> df <- data.frame(a = c(1,2,3,4,4,4,3,5,7), 
                   b=c(12,13,14,15,15,16,17,22,18),
                   c=c(1,1,1,1,2,1,1,1,1),
                   e=c("cat1", "cat2", "cat1", "cat1", "cat2", "cat3", "cat2", "cat1", "cat2"))
> df$e <- as.character(df$e)

# create index you'd like to group by
> df$ab <- paste(df$a, df$b)

> library(plyr)
> ddply(df, .(ab), summarize, f = list(e), g = list(c))

    ab          f    g
1 1 12       cat1    1
2 2 13       cat2    1
3 3 14       cat1    1
4 3 17       cat2    1
5 4 15 cat1, cat2 1, 2
6 4 16       cat3    1
7 5 22       cat1    1
8 7 18       cat2    1

从data.table的组中获取行

2 个答案: