Question

dplyr::select会生成一个data.frame，如果结果是一列，有没有办法让它返回一个向量？

目前，我必须执行额外步骤（res <- res$y）将其转换为data.frame中的vector，请参阅此示例：

#dummy data
df <- data.frame(x = 1:10, y = LETTERS[1:10], stringsAsFactors = FALSE)

#dplyr filter and select results in data.frame
res <- df %>% filter(x > 5) %>% select(y)
class(res)
#[1] "data.frame"

#desired result is a character vector
res <- res$y
class(res)
#[1] "character"

如下所示：

res <- df %>% filter(x > 5) %>% select(y) %>% as.character
res
# This gives strange output
[1] "c(\"F\", \"G\", \"H\", \"I\", \"J\")"

# I need:
# [1] "F" "G" "H" "I" "J"

Answer 1

最佳方式（IMO）：

library(dplyr)
df <- data_frame(x = 1:10, y = LETTERS[1:10])

df %>% 
  filter(x > 5) %>% 
  .$y

在dplyr 0.7.0中，您现在可以使用pull（）：

df %>% filter(x > 5) %>% pull(y)

Answer 2

这样的东西？

> res <- df %>% filter(x>5) %>% select(y) %>% sapply(as.character) %>% as.vector
> res
[1] "F" "G" "H" "I" "J"
> class(res)
[1] "character"

Answer 3

您也可以尝试

res <- df %>%
           filter(x>5) %>%
           select(y) %>%
           as.matrix() %>%
           c()
#[1] "F" "G" "H" "I" "J"

 class(res)
#[1] "character"

dplyr ::选择一列并输出为向量

3 个答案: