如何基于两列组合两个数据框? [英] How do I combine two data-frames based on two columns?

问题描述

我知道我可以使用 plyr 和它的朋友来组合数据帧，以及 merge，但到目前为止我不知道如何将两个数据帧与基于 2 列的多列?

I know I can use the plyr and its friends to combine dataframes, and merge as well, but so far I don't know how to merge two dataframes with multiple columns based on 2 columns?

推荐答案

请参阅关于 ?merge 的文档，其中指出:

See the documentation on ?merge, which states:

By default the data frames are merged on the columns with names they both have, 
 but separate specifications of the columns can be given by by.x and by.y.

这清楚地暗示 merge 将合并基于多列的数据帧.从文档中给出的最后一个例子:

This clearly implies that merge will merge data frames based on more than one column. From the final example given in the documentation:

x <- data.frame(k1=c(NA,NA,3,4,5), k2=c(1,NA,NA,4,5), data=1:5)
y <- data.frame(k1=c(NA,2,NA,4,5), k2=c(NA,NA,3,4,5), data=1:5)
merge(x, y, by=c("k1","k2")) # NA's match

此示例旨在演示 incomparables 的使用，但它也说明了使用多列的合并.您还可以使用 by.x 和 by.y 在 x 和 y 中的每一个中指定单独的列.

This example was meant to demonstrate the use of incomparables, but it illustrates merging using multiple columns as well. You can also specify separate columns in each of x and y using by.x and by.y.

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