如何在 R 中使用星号符号 select 变量

Question

I want to select some variables from my csv file in R. I used this select(gender*, age*) , but got the error - object not found. I tried select(`gender*`, `age*`) and select(starts_with(gender), starts_with(age)) , but neither works. Does anyone know how to select variables with star symbols? Thanks a lot!

Answer 1

It is possible that the select from dplyr is masked by select from any other package as this is working fine. Either specify the packagename with :: or do this on a fresh R session with only dplyr loaded

library(dplyr)
data(iris)
iris$'gender*' <- 'M'
iris%>% 
      head %>% 
      dplyr::select(`gender*`)
#   gender*
#1       M
#2       M
#3       M
#4       M
#5       M
#6       M

Answer 2

To select a list of column names starting with a specific string, one can use the starts_with() function in dplyr . To illustrate, we'll select the two columns that start with the string Sepal , as in Sepal.Length and Sepal.Width .

library(dplyr)
select(iris,starts_with("Sepal")) %>% head()

...and the output:

> select(iris,starts_with("Sepal")) %>% head()
  Sepal.Length Sepal.Width
1          5.1         3.5
2          4.9         3.0
3          4.7         3.2
4          4.6         3.1
5          5.0         3.6
6          5.4         3.9
>

We can do the same thing in Base R with grepl() and a regular expression.

# base R version
head(iris[,grepl("^Sepal",names(iris))])

...and the output:

> head(iris[,grepl("^Sepal",names(iris))])
  Sepal.Length Sepal.Width
1          5.1         3.5
2          4.9         3.0
3          4.7         3.2
4          4.6         3.1
5          5.0         3.6
6          5.4         3.9
>

Also note that if one is using read.csv() to create a data frame in R, it converts any occurrences of * in column headings to . .

# confirm that * is converted to . in read.csv()
textFile <- 'v*1,v*2
1,2
3,4
5,6'
data <- read.csv(text = textFile,header = TRUE)
# see how illegal column name * is converted to . 
names(data)

...and the output:

> names(data)
[1] "v.1" "v.2"
>