R：基於所有行的每行的條件

Question

行的每個值如何與每個表的值進行比較？更具體地說，假設我有下表：

DT = data.table(x=rep(c("a","b","c"),each=3), y=c(1,3,6), 
    v=1:9,w=as.integer(rnorm(9)*10)) 

> DT 
## x y v w 
## 1: a 1 1 0 
## 2: a 3 2 0 
## 3: a 6 3 6 
## 4: b 1 4 -4 
## 5: b 3 5 -27 
## 6: b 6 6 10 
## 7: c 1 7 4 
## 8: c 3 8 1 
## 9: c 6 9 7 

我怎麼能找到w的數量大於每個w？ 所需的輸出：

> DT1 
## x y v w count 
## 1: a 1 1 0 2 # 0 is greater than -4 and -27 
## 2: a 3 2 0 2 
## 3: a 6 3 6 6 
## 4: b 1 4 -4 1 
## 5: b 3 5 -27 0 
## 6: b 6 6 10 8 
## 7: c 1 7 4 6 
## 8: c 3 8 1 3 
## 9: c 6 9 7 7 

Answer 1

舉例如下：

set.seed(123) 
DT$count <- sapply(DT$w, function(x) sum(x > DT$w)) 
DT 
    x y v w count 
1: a 1 1 -5  2 
2: a 3 2 -2  3 
3: a 6 3 15  7 
4: b 1 4 0  4 
5: b 3 5 1  5 
6: b 6 6 17  8 
7: c 1 7 4  6 
8: c 3 8 -12  0 
9: c 6 9 -6  1 

Answer 2

您可以ties.method = "min"一起使用rank。

DT[, count := rank(w, ties.method = 'min') - 1]