R-使用另一个数据框的匹配值将新列添加到数据框 [英] R - Add a new column to a dataframe using matching values of another dataframe

问题描述

我正在尝试用匹配的table2的val2值填充table1

I am trying to fill in table1 with matching val2 values of table2

table1$New_val2 = table2[table2$pid==table1$pid,]$val2

但是我得到警告

longer object length is not a multiple of shorter object length

这很公平，因为表的长度不同.

which is fair enough because the table lengths are not the same.

请指导我正确的方法.

推荐答案

merge(table1, table2[, c("pid", "col2")], by="pid")

添加all.x=TRUE参数，以便将table1中所有不匹配的pid保留在table2中.

Add in the all.x=TRUE argument in order to keep all of the pids in table1 that don't have matches in table2.

您在正确的轨道上.这是使用match的一种方法...

You were on the right track. Here's a way using match...

table1$val2 <- table2$val2[match(table1$pid, table2$pid)]

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