Question

我有两个data.frames dfA和dfB。他们两个都有一个名为key的列。现在，我想知道B $ key中有多少A $ key重复项。

A <- data.frame(key=c("A", "B", "C", "D"))
B <- data.frame(key=c("A", "A", "B", "B", "B", "D"))

应为A = 2，B = 3，C = 0和D = 1。最简单的方法是什么？

Answer 1

使用table

table(factor(B$key, levels = sort(unique(A$key))))
#A B C D 
#2 3 0 1

在这里需要

factor，这样我们也可以“计数”未出现在B$key中的条目，即C。

Answer 2

您可以使用tidyverse：

A %>%
 left_join(B %>% #Merging df A with df B for which the count in "key" was calculated
            group_by(key) %>%
            tally(), by = c("key" = "key")) %>%
 mutate(n = ifelse(is.na(n), 0, n)) #Replacing NA with 0

  key n
1   A 2
2   B 3
3   C 0
4   D 1

Answer 3

A <- data.frame(key=c("A", "B", "C", "D"))
B <- data.frame(key=c("A", "A", "B", "B", "B", "D"))

library(dplyr)
library(tidyr)

B %>%
  filter(key %in% A$key) %>%                 # keep values that appear in A
  count(key) %>%                             # count values
  complete(key = A$key, fill = list(n = 0))  # add any values from A that don't appear

# # A tibble: 4 x 2
#   key       n
#   <chr> <dbl>
# 1 A         2
# 2 B         3
# 3 C         0
# 4 D         1

Answer 4

实际上，您是指在A$key中每个B$key值出现多少次？

您可以通过将B$key的唯一值作为级别编码为因子来A$key。

o <- table(factor(B$key, levels=unique(A$key)))

产量：

> o

A B C D 
2 3 0 1

如果您真的想计算重复次数，请

dupes <- ifelse(o - 1 < 0, 0, o - 1)

产量：

> dupes

A B C D 
1 2 0 0

计算其他数据框中的重复项数量

4 个答案: