[英]Pass column names as argument into a function
I created a data table df
我创建了一个数据表
df
library(data.table)
df <- data.table(id = c(1,1,1,2,2), starts = c(0,0,6,0,9), ends = c(0,6,10,9,20))
df
#id starts ends
#1: 1 0 0
#2: 1 0 6
#3: 1 6 10
#4: 2 0 9
#5: 2 9 20
I defined a function 'equal_0', which is entering a col_name
, then the function would return a data table with that col_name == 0
我定义了一个函数“equal_0”,它输入一个
col_name
,然后该函数将返回一个带有col_name == 0
的数据表
equal_0 <- function(col_name){
a <- df[col_name == 0]
return(a)
}
For example, equal_0(starts)
equals to df[starts == 0]
, the expected result is:例如,
equal_0(starts)
等于df[starts == 0]
,预期结果是:
df[starts==0]
#id starts ends
#1: 1 0 0
#2: 1 0 6
#3: 2 0 9
However, both equal_0(starts)
and equal_0("starts")
don't work.但是,
equal_0(starts)
和equal_0("starts")
都不起作用。
The error message is:错误信息是:
equal_0("starts")
#Empty data.table (0 rows) of 3 cols: id,starts,ends
equal_0(starts)
#Error in eval(.massagei(isub), x, parent.frame()) : object 'starts' not found
How can I pass starts
into the function equal_0
?如何将
starts
传递到函数equal_0
?
Use get
to extract column from the data.table:使用
get
从 data.table 中提取列:
equal_0 <- function(col_name){
library(data.table)
a <- df[get(col_name) == 0]
return(a)
}
equal_0("starts")
id starts ends
1: 1 0 0
2: 1 0 6
3: 2 0 9
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