基于数据框中的多列查找值

尝试使用左连接 merge

merge(df1, df2, by = 1:2, all.x = TRUE)

给:

  g1 g2 val
1  a  1 100
2  b  2 200
3  c  3  NA
4  c  4 300

有些备选方案是:

transform(df1, val = df2$val[match(paste(g1, g2), paste(df2$g.1, df2$g.2))])

library(sqldf)
sqldf("select df1.*, df2.val 
       from df1 left join df2 on g1 = [g.1] and g2 = [g.2]")

library(dplyr)
df1 %>% left_join(df2, by = c(g1 = "g.1", g2 = "g.2"))

一个加入会更好,而且更具吸引力 data.table ,当我们更新我的参考资料时,它会变得更有效

library(data.table)
setDT(df1)[df2, value := val, on = .(g1 = g.1, g2 = g.2)]
df1
#    g1 g2 value
#1:  a  1   100
#2:  b  2   200
#3:  c  3    NA
#4:  c  4   300

具有 match ,一种方法是 paste 将感兴趣的列放在一起,然后创建一个索引来更改值

p1 <- do.call(paste, df1)
p2 <- do.call(paste, df2[1:2])
i1 <- match(p1, p2, nomatch = 0)
i2 <- match(p2, p1, nomatch = 0)
df1$value[i2] <- df2$val[i1]
df1
#  g1 g2 value
#1  a  1   100
#2  b  2   200
#3  c  3    NA
#4  c  4   300

根据@G.Grothendieck的回答,我发现我做错了什么。我所要做的就是:

df1$value <- df2[match(paste0(df1$g1,df1$g2), paste0(df2$g.1,df2$g.2)),]$val