如何使用用户输入的数字作为变量？

Question

我有8个变量作为Var1-Var8。我想根据用户的选择找到他们中的2个之间的交叉产品。我从用户那里获取了2个输入，当它试图计算时，结果无法计算，因为找不到Var(x)。如何将用户的输入作为函数中的变量。我尝试了Var(x)，Varx和Var$x，但它不起作用。已经谢谢你了。

findCrossProduct=function(x,y){

  print("which variables do you want to see the cross-product between ?")
  x=readline("Enter the first variable :")
  y=readline("Enter the second variable :")

  >> cp=sum(Var(x)*Var(y))-(sum(Var(x)*sum(Var(y))/length(Var(y)))) 

  print(paste("Cross-product betwen variable ",x,"and variable",y,"is",cp))

}

Answer 1

应该在函数中调用整个数据帧。

findCrossProduct=function(df){

  print("which variables do you want to see the cross-product between?")

  x = readline("Enter the first variable: ")
  y = readline("Enter the second variable: ")

  cp = sum(df[x] * df[y]) - (sum(df[x])*sum(df[y])/nrow(df[y])) 

  print(paste("Cross-product between variable", x, "and variable", y, "is", cp))

}

输出为

> findCrossProduct(data)
[1] "which variables do you want to see the cross-product between?"
Enter the first variable: Var2
Enter the second variable: Var3
[1] "Cross-product between variable Var2 and variable Var3 is 0.200000000000045"

确保我使用的叉积公式是正确的。