将字符串转换为 R 中 for 循环内的对象

Question

我希望能够使用以下构造在循环内查看 iris（内置数据集）几列的摘要输出，我看到了 here ，mget 可能是一个解决方案，但我猜它不是。有人可以在这里提供最新有效的方法运行吗

l <- c("Sepal.Length","Sepal.Width")

for(i in l){
    print(summary( mget(paste0("iris$",l))))
}

我在上面的运行ning 上收到错误消息

Error: value for ‘iris$Sepal.Length’ not found

Q2 这对于不同的数据帧如何工作

l <- c("iris","mtcars")
    
    for(i in l){
        print(summary( mget(l)))
    }

Answer 1

由于向量中包含列名，因此不需要 get。直接作为索引[[提取列即可

基数 R：

sapply(l, function(x) summary(iris[[x]]))
        Sepal.Length Sepal.Width
Min.        4.300000    2.000000
1st Qu.     5.100000    2.800000
Median      5.800000    3.000000
Mean        5.843333    3.057333
3rd Qu.     6.400000    3.300000
Max.        7.900000    4.400000

Q2:

在这种情况下，因为您需要 get 对象的值，所以您确实需要 get() 函数。

sapply(c("iris","mtcars"), function(x) summary(get(x)))

$iris
  Sepal.Length    Sepal.Width     Petal.Length    Petal.Width   
 Min.   :4.300   Min.   :2.000   Min.   :1.000   Min.   :0.100  
 1st Qu.:5.100   1st Qu.:2.800   1st Qu.:1.600   1st Qu.:0.300  
 Median :5.800   Median :3.000   Median :4.350   Median :1.300  
 Mean   :5.843   Mean   :3.057   Mean   :3.758   Mean   :1.199  
 3rd Qu.:6.400   3rd Qu.:3.300   3rd Qu.:5.100   3rd Qu.:1.800  
 Max.   :7.900   Max.   :4.400   Max.   :6.900   Max.   :2.500  
       Species  
 setosa    :50  
 versicolor:50  
 virginica :50  
                
                
                

$mtcars
      mpg             cyl             disp             hp       
 Min.   :10.40   Min.   :4.000   Min.   : 71.1   Min.   : 52.0  
 1st Qu.:15.43   1st Qu.:4.000   1st Qu.:120.8   1st Qu.: 96.5  
 Median :19.20   Median :6.000   Median :196.3   Median :123.0  
 Mean   :20.09   Mean   :6.188   Mean   :230.7   Mean   :146.7  
 3rd Qu.:22.80   3rd Qu.:8.000   3rd Qu.:326.0   3rd Qu.:180.0  
 Max.   :33.90   Max.   :8.000   Max.   :472.0   Max.   :335.0  
      drat             wt             qsec             vs        
 Min.   :2.760   Min.   :1.513   Min.   :14.50   Min.   :0.0000  
 1st Qu.:3.080   1st Qu.:2.581   1st Qu.:16.89   1st Qu.:0.0000  
 Median :3.695   Median :3.325   Median :17.71   Median :0.0000  
 Mean   :3.597   Mean   :3.217   Mean   :17.85   Mean   :0.4375  
 3rd Qu.:3.920   3rd Qu.:3.610   3rd Qu.:18.90   3rd Qu.:1.0000  
 Max.   :4.930   Max.   :5.424   Max.   :22.90   Max.   :1.0000  
       am              gear            carb      
 Min.   :0.0000   Min.   :3.000   Min.   :1.000  
 1st Qu.:0.0000   1st Qu.:3.000   1st Qu.:2.000  
 Median :0.0000   Median :4.000   Median :2.000  
 Mean   :0.4062   Mean   :3.688   Mean   :2.812  
 3rd Qu.:1.0000   3rd Qu.:4.000   3rd Qu.:4.000  
 Max.   :1.0000   Max.   :5.000   Max.   :8.000

将字符串转换为 R 中 for 循环内的对象

Convert string as object inside for loop in R

r

dplyr

tidyverse