[英]Reference R data frame column name as a string, given only the column name
I have a data frame df.我有一个数据框 df。 It has a column named
b
.它有一个名为
b
的列。 I know this column name, although I do not know its position in the data frame.我知道这个列名,虽然我不知道它在数据框中的 position。 I know that colnames(df) will give me a vector of character strings that are the names of all the columns, but I do not know how to get a string for this particular column.
我知道 colnames(df) 会给我一个字符串向量,它是所有列的名称,但我不知道如何获取这个特定列的字符串。 In other words, I want to obtain the string "b".
换句话说,我想获得字符串“b”。 How can I do that?
我怎样才能做到这一点? I imagine this may involve the rlang package, which I have difficulty understanding.
我想这可能涉及我难以理解的 rlang package。
Here's an example:这是一个例子:
library(rlang)
library(tidyverse)
a <- c(1:8)
b <- c(23,34,45,43,32,45,68,78)
c <- c(0.34,0.56,0.97,0.33,-0.23,-0.36,-0.11,0.17)
df <- data.frame(a,b,c)
tf <- function(df,MYcol) {
print(paste0("The name of the input column is ",MYcol)) # does not work
print(paste0("The name of the input column is ",{{MYcol}})) # does not work
y <- {{MYcol}} # This gives the values in column b as it shoulkd
}
z <- tf(df,b) # Gives undesired values - I want the string "b"
We can use as_string
with enquo/ensym
我们可以将
as_string
与enquo/ensym
一起使用
tf <- function(df, MYcol) {
mycol <- rlang::as_string(rlang::ensym(MYcol))
print(glue::glue("The name of the input column is {mycol}"))
return(mycol)
}
z <- tf(df,b)
The name of the input column is b
z
#[1] "b"
If you cannot pass column name as string in the function ( tf(df,"b")
) directly, you can use deparse
+ substitute
.如果不能直接在 function (
tf(df,"b")
) 中将列名作为字符串传递,则可以使用deparse
+ substitute
。
tf <- function(df,MYcol) {
col <- deparse(substitute(MYcol))
print(paste0("The name of the input column is ",col))
return(col)
}
z <- tf(df,b)
#[1] "The name of the input column is b"
z
#[1] "b"
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