在 R 中获取新变量的问题

Question

这是我第一次发帖，请多多包涵。我正在尝试通过基于现有数据添加新列来操作 R 中的数据集。我已将数据转换为数据框并使用了 mutate 函数。该功能有效。但是，当我再次调用我的数据集以查看更改时，新列消失了。我做错了什么？

# Converting raw data into a tibble data frame for easier data analysis:
spdata <- as_tibble(rawdata)

# Creating a new Grade column based on Math Scores
spdata %>%
    mutate(math.grade = case_when(math.score < 60 ~ "F",
                                  math.score >= 60 & math.score <= 69 ~ "D",
                                  math.score >= 70 & math.score <= 79 ~ "C",
                                  math.score >= 80 & math.score <= 89 ~ "B",
                                  math.score >= 90 & math.score <= 100 ~ "A"))

这是我运行 mutate 函数后自动生成的输出：

# A tibble: 1,000 x 9
   gender race.ethnicity parental.level.of.education lunch        test.preparation.course math.score reading.score writing.score math.grade
   <fct>  <fct>          <fct>                       <fct>        <fct>                        <int>         <int>         <int> <chr>     
 1 female group B        bachelor's degree           standard     none                            72            72            74 C         
 2 female group C        some college                standard     completed                       69            90            88 D         
 3 female group B        master's degree             standard     none                            90            95            93 A         
 4 male   group A        associate's degree          free/reduced none                            47            57            44 F         
 5 male   group C        some college                standard     none                            76            78            75 C         
 6 female group B        associate's degree          standard     none                            71            83            78 C         
 7 female group B        some college                standard     completed                       88            95            92 B         
 8 male   group B        some college                free/reduced none                            40            43            39 F         
 9 male   group D        high school                 free/reduced completed                       64            64            67 D         
10 female group B        high school                 free/reduced none                            38            60            50 F         
# ... with 990 more rows

我的新 math.grade 变量按预期显示。

但是，当我再次调用 spdata 查看时，math.grade 列不见了：

# A tibble: 1,000 x 8
   gender race.ethnicity parental.level.of.education lunch        test.preparation.course math.score reading.score writing.score
   <fct>  <fct>          <fct>                       <fct>        <fct>                        <int>         <int>         <int>
 1 female group B        bachelor's degree           standard     none                            72            72            74
 2 female group C        some college                standard     completed                       69            90            88
 3 female group B        master's degree             standard     none                            90            95            93
 4 male   group A        associate's degree          free/reduced none                            47            57            44
 5 male   group C        some college                standard     none                            76            78            75
 6 female group B        associate's degree          standard     none                            71            83            78
 7 female group B        some college                standard     completed                       88            95            92
 8 male   group B        some college                free/reduced none                            40            43            39
 9 male   group D        high school                 free/reduced completed                       64            64            67
10 female group B        high school                 free/reduced none                            38            60            50
# ... with 990 more rows

Answer 1

您需要将带有附加列的数据框分配给带有<- 的新变量：

new_df <- spdata %>%
    mutate(math.grade = case_when(math.score < 60 ~ "F",
                                  math.score >= 60 & math.score <= 69 ~ "D",
                                  math.score >= 70 & math.score <= 79 ~ "C",
                                  math.score >= 80 & math.score <= 89 ~ "B",
                                  math.score >= 90 & math.score <= 100 ~ "A"))
new_df

这应该可以...