why does atomic operator $ work with character, but not character stored in variable?-CodePudding

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why does atomic operator $ work with character, but not character stored in variable?

Time：12-11

I have a dataframe called "groups", with column names "A" through "H".

Any idea what's the problem with this and how to fix it?


for(i in colnames(groups)){

   print(groups$i)

}


> NULL
> NULL
> NULL
> NULL
> NULL
> NULL
> NULL
> NULL

Especifically, why is this so?


groups$"A"


> "Ecuador"
> "Netherlands"
> "Qatar"
> "Senegal"



i <- "A"

groups$i


> NULL

CodePudding user response：

Here is the solution:

for(i in 1:length(groups)){
  print(groups[i])
  }