[英]R- random sample of groups in a data.table
如何在data.table中隨機采樣例如三組,以使結果包含三組,其中原始data.table中的所有行均如此?
library(data.table)
dat <- data.table(ids=1:20, groups=sample(x=c("A","B","C", "D", "E", "F"), 20,
replace=TRUE))
我知道如何從data.table中隨機選擇10行:
dat.sampl1 <- as.data.table(sapply(dat[], sample, 10))
還有如何按組抽樣
dat[,.SD[sample(.N, min(.N,3))], by = groups]
但是如何隨機分組? 因此結果應如下所示:
ids groups
1 F
11 F
3 F
18 F
8 A
9 A
10 A
17 A
19 A
12 E
14 E
16 E
您的意思是:
set.seed(123)
dat <- data.table(ids=1:20, groups=sample(x=c("A","B","C", "D", "E", "F"), 20,
replace=TRUE))
dat[groups %in% sample(unique(dat[, groups]), size = 3)][order(groups)]
# ids groups
# 1: 3 C
# 2: 10 C
# 3: 12 C
# 4: 7 D
# 5: 9 D
# 6: 14 D
# 7: 4 F
# 8: 5 F
# 9: 8 F
# 10: 11 F
# 11: 16 F
# 12: 20 F
如果要對具有replacement的組進行抽樣,則可以執行以下操作,其中對A
進行了兩次抽樣:
dat[unique(dat[, list(groups)])[sample(.N, 3, replace = TRUE)], on = "groups"]
# ids groups
# 1: 3 C
# 2: 10 C
# 3: 12 C
# 4: 6 A
# 5: 15 A
# 6: 18 A
# 7: 6 A
# 8: 15 A
# 9: 18 A
此代碼有效,使用單行基礎R代碼(使用%in%
檢查使用sample
函數生成的索引:
df1[df1[,'groups'] %in% sample(unique(df1[,'groups']), size = 3, replace = F), ]
例如:
> df1 <- data.frame("ids" = 1:20, "groups" = sample(LETTERS[1:4], size = 20, replace = T))
> df2 <- df1[df1[,'groups'] %in% sample(unique(df1[,'groups']), size = 3, replace = F), ]
> df2[order(df2[,'groups']),]
ids groups
4 4 B
6 6 B
18 18 B
20 20 B
1 1 C
2 2 C
3 3 C
9 9 C
12 12 C
16 16 C
19 19 C
7 7 D
11 11 D
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