小编Big*_*ger的帖子

我有一个稀疏数据表,如下所示:

 data = data.table(
    var1 = c("a","",""),
    var2 = c("","","c"),
    var3 = c("a","b",""),
    var4 = c("","b","")
)
      var1 var2 var3 var4
    1:    a         a     
    2:              b    b
    3:         c     

我想添加一个包含一串零和一列的列,指示任何行中存在哪些变量,如下所示:

  var1 var2 var3 var4  concat
1:    a         a      1|0|1|0
2:              b    b 0|0|1|1
3:         c           0|1|0|0

我可以使用以下命令来实现此目的:

data[, concat := paste(
           as.integer(var1 != ""),
           as.integer(var2 != ""),
           as.integer(var3 != ""),
           as.integer(var4 != ""),
           sep = "|")]

但是,如果我有数百个变量,我宁愿使用某种计算来获得所需的表达式.也许基于paste0("var",1:4)或至少是列名称的向量.有什么建议？

我正在学习操作data.table变量的语法.虽然我可以做简单的事情,但我的理解对于更复杂的任务来说还不够彻底.例如,我想将以下数据转换为每行具有一个不同的"类型"值,基于"子类型"的值生成单独的列,并且当存在具有相同"类型/子类型的多个行时折叠唯一值"组合.

给定输入数据:

data = data.frame(
    var1 = c("a","b","c","b","d","e","f"),
    var2 = c("aa","bb","cc","dd","ee","ee","ff"),
    subtype = c("1","2","2","2","1","1","2"),
    type = c("A","A","A","A","B","B","B")
    )

  var1 var2 subtype type
1    a   aa       1    A
2    b   bb       2    A
3    c   cc       2    A
4    b   dd       2    A
5    d   ee       1    B
6    e   ee       1    B
7    f   ff       2    B

我想得出:

  1.var1 1.var2 2.var1 2.var2     2.type
A "a"    "aa"   "b|c"  "bb|cc|dd" "A"   
B "d|e"  "ee"   "f"    "ff"       "B"   

使用数据框,我可以使用以下代码实现此目的:

data.derived = do.call(
    rbind, …