计算每一列的唯一值

我想返回表中每一列的唯一值的计数。例如，如果我有表：

I would like to return the count of the unique values for every column in a table. For example, if I have the table:

 Testdata <- data.frame(var_1 = c("a","a","a"), var_2 = c("b","b","b"), var_3 = c("c","d","e"))

 var_1 | var_2 | var_3
 a     | b     | c 
 a     | b     | d
 a     | b     | e

我希望输出为：

 Variable | Unique_Values
 var_1    | 1
 var_2    | 1
 var_3    | 3

我尝试使用唯一功能来处理循环，例如

I have tried playing around with loops using the unique function, e.g.

 for(i in names(Testdata)){
    # Code using unique function
 }

但是我怀疑有更简单的方法。

However I suspect there is a simpler way.