[R] colMeans function

[Marc Schwartz]

Hi,

You might want to become familiar with the ?str and ?dim functions, which can help you identify the structure of the objects that you are passing to colMeans().

In the first case, flights[2] is a data frame with a single column, so will have two dimensions with a row and column structure.

In the second case, flights$month is a single numeric vector within the data frame and does not have a row and column dimension structure.

If you used flights[[2]], that would be equivalent to flights$month, in referencing a single numeric vector.

So, if you used:

str(flights[2])
dim(flights[2])

str(flights$month)
dim(flights$month)

you would see the difference.

Regards,

Marc Schwartz


> On Nov 4, 2020, at 8:26 AM, Engin Yılmaz <ispanyolcom using gmail.com> wrote:
> 
> Dear
> I use *flights* database library(nycflights13)
> 
> The following code is working as
> 
> colMeans(flights[2])
> 
> * 6.54851*
> 
> but other code is  not working as
> 
> colMeans(flights$month)
> 
> *Error in colMeans(flights$month) : *
> *  'x' must be an array of at least two dimensions*
> 
> *flights[2]* is equal to the *month *column in database
> 
> *Sincerely*
> Engin YILMAZ