r表示整個數據的數據更新列的子集

Question

我希望計算數據子集的一列的平均值，並將該平均值輸入到整個數據的新列中。

下面是一些代碼，以使事情更清晰的希望：

t <- data.table(Label=c(0,1,0,1,1,1), x=c("aa","aa","aa","aa","bb","bb"), environment=c("train","train","test","test","train","test")) 
t 
    Label x environment 
1:  0 aa  train 
2:  1 aa  train 
3:  0 aa  test 
4:  1 aa  test 
5:  1 bb  train 
6:  1 bb  test 
setkey(t,x) 
t[environment=="train",avg := mean(Label),by=c("x")] 

t 
    Label x environment avg 
1:  0 aa  train 0.5 
2:  1 aa  train 0.5 
3:  0 aa  test NA 
4:  1 aa  test NA 
5:  1 bb  train 1.0 
6:  1 bb  test NA 

以上，除了它的作品不更新行的代碼，其中環境==「測試」，因爲我做的平均值這是正常的不包括那些子集。

所以我想保留子集上的平均值，但更新所有行的平均值列，包括「測試」列。

所以結果應該是：

t 
    Label x environment avg 
1:  0 aa  train 0.5 
2:  1 aa  train 0.5 
3:  0 aa  test 0.5 # average calculated with train rows only 
4:  1 aa  test 0.5 # average calculated with train rows only 
5:  1 bb  train 1.0 
6:  1 bb  test 1.0 # average calculated with train rows only 

Answer 1

好像這是你以後有什麼

t[environment == "train", avg := mean(Label), by = x][, avg := mean(avg, na.rm = T), by= x] 
t 

## Label x environment avg 
## 1:  0 aa  train 0.5 
## 2:  1 aa  train 0.5 
## 3:  0 aa  test 0.5 
## 4:  1 aa  test 0.5 
## 5:  1 bb  train 1.0 
## 6:  1 bb  test 1.0 

Answer 2

你也許可以解決只用data.table這個問題，但對我來說最快捷，最方便的方法得到想要的答案是使用na.locf function from zoo

require(data.table) 
require(zoo) 
t <- data.table(Label=c(0,1,0,1,1,1), x=c("aa","aa","aa","aa","bb","bb"), environment=c("train","train","test","test","train","test")) 

t[environment=="train",avg := mean(Label),by=c("x")] 
t[,avg:=na.locf(avg),by=c("x")] 

只是爲了表明它的工作原理，我添加了一個額外的亂序測試用例，標籤值爲5（使得用組分隔的手段大不相同）。這是我得到的輸出。

t <- data.table(Label=c(0,1,0,1,1,1,5), x=c("aa","aa","aa","aa","bb","bb","aa"), environment=c("train","train","test","test","train","test","test")) 

t[environment=="train",avg := mean(Label),by=c("x")] 
t[,avg:=na.locf(avg),by=c("x")] 
t 
    Label x environment avg 
1:  0 aa  train 0.5 
2:  1 aa  train 0.5 
3:  0 aa  test 0.5 
4:  1 aa  test 0.5 
5:  1 bb  train 1.0 
6:  1 bb  test 1.0 
7:  5 aa  test 0.5