基於因子水平和隨機選擇創建新變量

Question

我有點卡住試圖使用sample函數爲我的任務，這是從一個因子的每個級別的n抽樣隨機行，並創建一個新的變量對此和另一個變量的值。

簡化示例：

Subject = c("100","100","100","100", "100", "200", "200", "200", "200", "200") 
Condition = c("Blue","Blue","Blue","Blue", "Blue", "Blue", "Blue", "Blue", "Blue", "Blue") 
Response = rnorm(10) 
df = data.frame(Subject,Condition, Response) 

在這裏，目標將是採樣3點隨機的行爲的Subject每個級別，創建一個新的變量，假設Condition.Rand具有標記爲「紅」隨機選擇的行和其餘的標有無論什麼價值的都在Condition - 在這種情況下，「藍色」。因此對於每個Subject，60％的Condition.Rand將被標記爲「紅色」並且40％被標記爲「藍色」。

爲了清楚起見，我想恰好 3標記爲「紅」對被檢體100隨機行（或5周的觀察的60％），並且恰好隨機排標記爲「紅」對主題200

謝謝！

Answer 1

split使用劃分df爲子組和sample"Red"和"Blue"具有用於每個子組期望概率。

set.seed(42) 
do.call(rbind, lapply(split(df, df$Subject), function(a) 
cbind(a, 
    cond.rand = sample(c("Red","Blue"), size = nrow(a), replace = TRUE, prob = c(0.6,0.4))))) 
#  Subject Condition Response cond.rand 
#100.1  100  Blue -1.7813084  Blue 
#100.2  100  Blue -0.1719174  Blue 
#100.3  100  Blue 1.2146747  Red 
#100.4  100  Blue 1.8951935  Blue 
#100.5  100  Blue -0.4304691  Blue 
#200.6  200  Blue -0.2572694  Red 
#200.7  200  Blue -1.7631631  Blue 
#200.8  200  Blue 0.4600974  Red 
#200.9  200  Blue -0.6399949  Blue 
#200.10  200  Blue 0.4554501  Blue 

Answer 2

我們也可以用ave從base R

set.seed(42) 
df1$cond.rand <- with(df, ave(seq_along(Subject), Subject, FUN = function(x) 
    sample(c("Red", "Blue"), size = length(x), replace = TRUE, prob = c(0.6, 0.4)))) 
df1$cond.rand 
#[1] "Blue" "Blue" "Red" "Blue" "Blue" "Red" "Blue" "Red" "Blue" "Blue"