r - 使用嵌套条件提取 data.frame 中的随机行样本

Answer 1

I'd use which to get the vector of rows numbers from which you can sample given your condition....

iris[ sample( which( iris$Species != "setosa" ) , 2 ) , ]
#    Sepal.Length Sepal.Width Petal.Length Petal.Width    Species
#59           6.6         2.9          4.6         1.3 versicolor
#133          6.4         2.8          5.6         2.2  virginica

Answer 2

With dplyr:

library(dplyr)
set.seed(12)
filter(iris, Species != "setosa") %>% sample_n(., 2) 

Output:

   Sepal.Length Sepal.Width Petal.Length Petal.Width    Species
7           6.3         3.3          4.7         1.6 versicolor
81          7.4         2.8          6.1         1.9  virginica

Answer 3

It'd be cleaner to not do it in one line, but

iris[iris$Species != "setosa",][sample(nrow(iris[iris$Species != "setosa",]), 2), ]

Answer 4

Clean and simple data table approach:

require(data.table)
iris <- data.table(iris)
cond <- iris[Species!= 'setosa', which = T]
iris[sample(cond, 2)]