r - 自定义函数为 dplyr 的 mutate 中的所有行返回相同的值

Question

我有以下数据:

                                                 Name
1                             Braund, Mr. Owen Harris
2 Cumings, Mrs. John Bradley (Florence Briggs Thayer)
3                              Heikkinen, Miss. Laina
4        Futrelle, Mrs. Jacques Heath (Lily May Peel)
5                            Allen, Mr. William Henry

数据可以这样加载:

structure(list(Name = c("Braund, Mr. Owen Harris", "Cumings, Mrs. John Bradley (Florence Briggs Thayer)", 
"Heikkinen, Miss. Laina", "Futrelle, Mrs. Jacques Heath (Lily May Peel)", 
"Allen, Mr. William Henry")), .Names = "Name", row.names = c(NA, 
-5L), class = c("tbl_df", "tbl", "data.frame"))

我的预期输出是:

                                                 Name    Title
1                             Braund, Mr. Owen Harris       Mr
2 Cumings, Mrs. John Bradley (Florence Briggs Thayer)      Mrs
3                              Heikkinen, Miss. Laina      Mrs
4        Futrelle, Mrs. Jacques Heath (Lily May Peel)      Mrs
5                            Allen, Mr. William Henry       Mr

问题是下面的代码会将所有 Title 设置为 “Mr”。我正在使用带有 dplyr 的 mutate 的自定义函数。

library('stringr')
library('dplyr')

extractTitle <- function(name) {
  str_match(name, '(\\b[a-zA-z]+)\\.')[2]
}

data <- data %>% 
          mutate(Title = extractTitle(Name))

奇怪的是，如果我更改 extractTitle 以按原样返回参数，它会按预期工作。例如:

extractTitle <- function(name) {
  name
}

data <- data %>% 
          mutate(Title = extractTitle(Name))

上面的代码会返回:

                                                 Name    Title
1                             Braund, Mr. Owen Harris   Braund, Mr. Owen Harris
2 Cumings, Mrs. John Bradley (Florence Briggs Thayer)   Cumings, Mrs. John Bradley (Florence Briggs Thayer)
3                              Heikkinen, Miss. Laina   Heikkinen, Miss. Laina
4        Futrelle, Mrs. Jacques Heath (Lily May Peel)   Futrelle, Mrs. Jacques Heath (Lily May Peel)
5                            Allen, Mr. William Henry   Allen, Mr. William Henry

这是我预期的行为，与我遇到问题的代码的行为不同。

我在这里遗漏了什么或者这是一个错误吗？

附言- 我正在使用 dplyr 版本 0.5.0

Answer 1

library(dplyr)
library(stringr)    
data %>%
      mutate(title = str_extract(string = Name, pattern = "(Mr|Miss|Mrs)\\.")) %>%
      select(Name, title)

返回:

# A tibble: 6 x 2
                                                 Name title
                                                <chr> <chr>
1                             Braund, Mr. Owen Harris   Mr.
2 Cumings, Mrs. John Bradley (Florence Briggs Thayer)  Mrs.
3                              Heikkinen, Miss. Laina Miss.
4        Futrelle, Mrs. Jacques Heath (Lily May Peel)  Mrs.
5                            Allen, Mr. William Henry   Mr.
6                                    Moran, Mr. James   Mr.