检查一个数据帧列中的值是否存在于第二个数据帧中 [英] Check whether values in one data frame column exist in a second data frame

问题描述

我有两个数据框（A和B），均带有 C列。我想检查数据帧B中的列'C'中的值是否存在于数据帧B中。

I have two data frames (A and B), both with a column 'C'. I want to check if values in column 'C' in data frame A exists in data frame B.

A = data.frame(C = c(1,2,3,4))
B = data.frame(C = c(1,3,4,7))

推荐答案

按如下方式使用％in％

A$C %in% B$C

哪个会告诉您A的C列的哪些值在B中。

Which will tell you which values of column C of A are in B.

返回的是逻辑向量。在您的示例的特定情况下，您将获得：

What is returned is a logical vector. In the specific case of your example, you get:

A$C %in% B$C
# [1]  TRUE FALSE  TRUE  TRUE

您可以将其用作<$ c $的行的索引c> A 或作为 A $ C 的索引以获取实际值：

Which you can use as an index to the rows of A or as an index to A$C to get the actual values:

# as a row index
A[A$C %in% B$C,  ]  # note the comma to indicate we are indexing rows

# as an index to A$C
A$C[A$C %in% B$C]
[1] 1 3 4  # returns all values of A$C that are in B$C

我们也可以取反：

A$C[!A$C %in% B$C]
[1] 2   # returns all values of A$C that are NOT in B$C

---

如果您想知道特定值是否在B $中C，使用相同的函数：

---

If you want to know if a specific value is in B$C, use the same function:

  2 %in% B$C   # "is the value 2 in B$C ?"  
  # FALSE

  A$C[2] %in% B$C  # "is the 2nd element of A$C in B$C ?"  
  # FALSE

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