不同长度的数据帧之间的条件匹配（如果 df1 中的两个值在 df2 中，则从 df2 中获取一个值）

问：

我有两个数据帧，df1 比 df2 短。两个数据帧之间有两个值重叠（重复）。按行，如果 df1 中的“Listener”与 df2 中的“Listener”行匹配，而 df1 中的“Trial”与 df2 中的“Trial”行匹配，则从 df2 中获取“PercCor”并将其放入 df1 中。

向量相当长（df1 是 147200 行，df2 是 510000），所以这是我的一些麻烦。

我希望这里有一个示例数据集，可能有助于阐明这个问题。

df1 <- data.frame(Listener = c("01JA","01JA","02JK","02JK", "03GL", "03GL"), Trial = c("Trial 1", "Trial 2", "Trial 1", "Trial 2", "Trial 1", "Trial 2"),
                  Pupil = c(1,2,4,3,2,6), Time = c(20, 40, 20, 40, 20, 40), percCor = c(NA, NA, NA, NA, NA, NA))
df2 <- data.frame(Listener = c("01JA","01JA","01JA","01JA", "01JA", "02JK","02JK","02JK","02JK", "02JK", "03GL", "03GL","03GL", "03GL", "03GL"), 
                 Trial = c("Trial 1", "Trial 1", "Trial 2", "Trial 2", "Trial 3","Trial 1", "Trial 1", "Trial 2", "Trial 2", "Trial 3","Trial 1", "Trial 1", "Trial 2", "Trial 2", "Trial 3"),
                 Pupil = c(1,1,1,2,4,3,2,6,2,5,6,2,4,5,6), Time = c(50, 100, 150, 50, 100, 150,50, 100, 150, 50, 100, 150, 50, 100, 150), percCor = c(100, 100, 20, 20, 60, 60, 60, 30, 30, 40, 60, 60, 40, 40, 55))

我正在寻找的答案是：

dfans <- data.framedf1 <- data.frame(Listener = c("01JA","01JA","02JK","02JK", "03GL", "03GL"), Trial = c("Trial 1", "Trial 2", "Trial 1", "Trial 2", "Trial 1", "Trial 2"),
                                     Pupil = c(1,2,4,3,2,6), Time = c(20, 40, 20, 40, 20, 40), percCor = c(100, 20, 60, 30, 60, 40))

我尝试了以下解决方案，但每种解决方案都遇到了问题。我似乎缺乏同时评估两个表达式的知识。我也尝试了 data.table 解决方案，但语法一直出错 - 我对它不是很熟悉:(

mdf <- merge(x=df1,y=df2, by.x=c("Listener","Trial"), by.y=c("Listener","Trial"))
#not enough RAM

mdf<-left_join(df1, df2, by= c('Listener','Trial'))%>%
   mutate(percCor=percCor.y)%>%
   select(-c(percCor.x,percCor.y))
#not enough RAM

mdf <-left_join(df1, df2)
#doesn't capture percCor

mdf <-right_join(df1, df2)
#keeps unnecessary trials/data

for(id in 1:nrow(df2)){
  df1$percCor[df1$Listener %in% df2$Listener[id]] <- df2$percCor[id]
}
#doesn't evaluate both Trial and Listener and is slow. 

for(id in 1:nrow(df2)){
  df1$percCor[df1$Listener %in% df2$Listener[id] & df1$Trial %in% df2$Trial] <- df2$percCor[id]
}
#not entirely sure why it seems to not evaluate both expressions at the same time. It only takes the listener's last percCor value for all trials. It's also incredibly slow. 

帮助？这感觉像是我应该知道如何做的事情......但我对 R 非常自学成才，老实说，尽管我已经在一些项目中使用了它，但我还是一个新手。我猜这不会那么困难 - 我花了半周时间查看 stackoverflow 答案 - 所以如果这很明显，我深表歉意。

感谢您的观看！