R 如何按组获取变量的所有最小值?
我有一个数据框:R 如何按组获取变量的所有最小值?,r,data.table,minimum,R,Data.table,Minimum,我有一个数据框: df<-data.frame(P = c("A","A","A", "B","B","B", "C", "C", "C"), index = c("ind1","ind2","ind3","ind1","ind2","ind3","ind1","ind2","ind3"), var = c(2,1,1,8,5,4,2,8,6)) 通过p,仅给出一个var的最小值(第一个): 我想: 想法?从which.min
df<-data.frame(P = c("A","A","A", "B","B","B", "C", "C", "C"),
index = c("ind1","ind2","ind3","ind1","ind2","ind3","ind1","ind2","ind3"),
var = c(2,1,1,8,5,4,2,8,6))
通过p
,仅给出一个var的最小值(第一个):
我想:
想法?从which.min
的帮助页面,您会注意到它说:
确定位置,即数字(或逻辑)向量的(第一个)最小值或最大值的索引
如果希望所有值都与最小值匹配,则应尝试使用=
。因此,继续您的方法,尝试:
DT[, .SD[var == min(var)], by = P]
## P index var
## 1: A ind2 1
## 2: A ind3 1
## 3: B ind3 4
## 4: C ind1 2
使用dplyr,可以使用以下选项之一:
library(dplyr)
DT %>% group_by(P) %>% filter(var == min(var)) # or %in% instead of ==
#Source: local data table [4 x 3]
#Groups: P
#
# P index var
# (fctr) (fctr) (dbl)
#1 A ind2 1
#2 A ind3 1
#3 B ind3 4
#4 C ind1 2
或
或
根据我的理解,您需要索引和P的每个唯一配对的最小值。。。然而,您想要的输出如何有两个P=='A'的观察值?然而,同时,根据同样的规则,对于P值“B”和“C”,你只有唯一的观察值。这应该会有所帮助
P index var
1: A ind2 1
2: A ind3 1
2: B ind3 4
3: C ind1 2
DT[, .SD[var == min(var)], by = P]
## P index var
## 1: A ind2 1
## 2: A ind3 1
## 3: B ind3 4
## 4: C ind1 2
library(dplyr)
DT %>% group_by(P) %>% filter(var == min(var)) # or %in% instead of ==
#Source: local data table [4 x 3]
#Groups: P
#
# P index var
# (fctr) (fctr) (dbl)
#1 A ind2 1
#2 A ind3 1
#3 B ind3 4
#4 C ind1 2
DT %>% group_by(P) %>% top_n(1, desc(var)) # top_n() returns multiple rows in case of ties
#Source: local data table [4 x 3]
#Groups: P
#
# P index var
# (fctr) (fctr) (dbl)
#1 A ind2 1
#2 A ind3 1
#3 B ind3 4
#4 C ind1 2
DT %>% group_by(P) %>% filter(min_rank(var) == 1)
#Source: local data table [4 x 3]
#Groups: P
#
# P index var
# (fctr) (fctr) (dbl)
#1 A ind2 1
#2 A ind3 1
#3 B ind3 4
#4 C ind1 2