What does a comma do in R?

Question

R

What does a comma give in this case: iris[, 3:5]compared with iris[3:5]like, the result is the same.

Also, what does such a case a[i, ]give?

Thanks

Answer 1

The construct a[, i]selects data by column i,
The construct a[i, ]selects row data i
a[i]works likea[, i]