`dcast`与空RHS [英] `dcast` with empty RHS

问题描述

有没有办法翻转我的数据，而不首先指定一个变量，要翻转？

例如，

  DT < -  data.table（id = rep（6:10，each = 3），var = rnorm（15））
 DT 
＃id var 
 ＃1：6 1.58293930 
＃2：6 0.44234019 
＃3：6 -0.06576521 
＃4：7 -0.65124980 
＃5：7 0.88371933 
＃ 7 -1.94998135 
＃7：8 -1.95746466 
＃8：8 -0.50978195 
＃9：8 -0.40450447 
＃10：9 -0.61097399 
＃11： 9 -0.92335213 
＃12：9 -0.19881983 
＃13：10 0.13022635 
＃14：10 -0.30141200 
＃15：10 0.78355188 
  

我想要的是基本上每个 id ，<$ c $在 id 中使用不同的列（ NA var 值关联），可以这样做：

  [，I：= 1：.N，by = id] #side note，为什么不是我：=。 
 dcast（DT，id〜I，value.var =var）
＃id 1 2 3 
＃1：6 1.5829393 0.4423402 -0.06576521 
＃2： 0.6512498 0.8837193 -1.94998135 
＃3：8 -1.9574647 -0.5097820 -0.40450447 
＃4：9 -0.6109740 -0.9233521 -0.19881983 
＃5：10 0.1302263 -0.3014120 0.78355188 
  

但是，如果我不必定义 I 首先，像这样：

  dcast（DT，id〜。，value.var =var）
  

但这不起作用：

缺少聚合函数，默认为'length'





 ＃id。 
＃1：6 3 
＃2：7 3 
＃3：8 3 
＃4：9 3 
＃5：10 3 
  

有没有可能的聚合函数，我可以传递来获得所需的效果？

rowid 函数：

pre> dcast（dt，id〜rowid（id），value.var =var）
＃id 1 2 3
＃1：6 1.1050942 0.1271620 1.3051373
＃2：7 -0.5441056 -0.6866828 -0.8083762
＃3：8 -0.6812820 -1.1934716 -1.3913903
＃4：9 -0.3462497 -0.8229276 -1.0884394
＃5：10 -0.4600681 0.6173795 -1.0125658


请参阅？rowid 以获得更多选项，示例和解释。

Is there any way to flip wide my data without first specifying a variable against which to be flipped? The logical default seems to me to be the in-group index.

For example,

DT <- data.table(id = rep(6:10, each = 3), var = rnorm(15))
DT
#     id         var
#  1:  6  1.58293930
#  2:  6  0.44234019
#  3:  6 -0.06576521
#  4:  7 -0.65124980
#  5:  7  0.88371933
#  6:  7 -1.94998135
#  7:  8 -1.95746466
#  8:  8 -0.50978195
#  9:  8 -0.40450447
# 10:  9 -0.61097399
# 11:  9 -0.92335213
# 12:  9 -0.19881983
# 13: 10  0.13022635
# 14: 10 -0.30141200
# 15: 10  0.78355188

What I want is basically, for each id, each value of var in a different column (and NAs if there's any id with fewer var values associated), which can be done like so:

DT[ , I := 1:.N, by = id] #side note, why doesn't I:=.I work??
dcast(DT, id ~ I, value.var = "var")
#    id          1          2           3
# 1:  6  1.5829393  0.4423402 -0.06576521
# 2:  7 -0.6512498  0.8837193 -1.94998135
# 3:  8 -1.9574647 -0.5097820 -0.40450447
# 4:  9 -0.6109740 -0.9233521 -0.19881983
# 5: 10  0.1302263 -0.3014120  0.78355188

However, it would be more convenient if I didn't have to define I first, like so:

dcast(DT, id~ ., value.var = "var")

But this doesn't work:

Aggregate function missing, defaulting to 'length'

#    id .
# 1:  6 3
# 2:  7 3
# 3:  8 3
# 4:  9 3
# 5: 10 3

Is there perhaps an aggregating function that I could pass to get the desired effect?

解决方案

This is now possible using the rowid function:

dcast(dt, id ~ rowid(id), value.var = "var")
#    id          1          2          3
# 1:  6  1.1050942  0.1271620  1.3051373
# 2:  7 -0.5441056 -0.6866828 -0.8083762
# 3:  8 -0.6812820 -1.1934716 -1.3913903
# 4:  9 -0.3462497 -0.8229276 -1.0884394
# 5: 10 -0.4600681  0.6173795 -1.0125658

See ?rowid for more options, examples, and explanation.

这篇关于`dcast`与空RHS的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！