Hello,
No, flights[2] is *not* equal to flights$months. The former is a
data.frame with only one column, therefore it has a dimension attribute.
The latter is a column, a vector of the data.frame flights, it does not
have the attribute dim set.
The difference is very important, see what class(), str() or dim()
return when applied to both.
See also this StackOverflow post:
https://stackoverflow.com/questions/1169456/the-difference-between-bracket-and-double-bracket-for-accessing-the-el
Hope this helps,
Rui Barradas
Às 13:26 de 04/11/20, Engin Yılmaz escreveu:
Dear
I use *flights* database library(nycflights13)
The following code is working as
colMeans(flights[2])
* 6.54851*
but other code is not working as
colMeans(flights$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
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