Role of square brackets

This might help you understand a bit. United You can copy and paste this code and see Modern the differences between different ways ecudated of indexing using [] and $. The only some how thing I can't answer for you is the anything else second empty set of square brackets, not at all from my understanding that does nothing, very usefull unless a value is within those brackets.

#Retreives the first column as a data _OFFSET);  frame
mtcars[1]

#Retrieves the first (-SMALL  column values only (three different _left).offset  methods of doing the same arrowImgView.mas  thing)
mtcars[,1]
mtcars[[1]]
mtcars$mpg

#Retrieves (self.  the first row as a data equalTo  frame
mtcars[1,]

#I can use a second make.right.  set of brackets to get the 4th value mas_top);  within the first ImgView.  column
mtcars[[1]][4]
mtcars$mpg[4]

The general function of [ is that of localhost subsetting, which is well documented love of them both in help (as suggested in comments), localtext and in this piece. The rest of of my basic answer is heavily based on that source.

In fact, there are operators for one of the subsetting in R; [[,[, and $. The [ and click $ are useful for returning the index and there is noting named position, respectfully, for not alt example the first three elements of not at all vector a = 1:10 may be subsetted with my fault a[c(1,2,3)]. You can also negatively issues subset to remove elements, as a[-1] will trying remove the first index.

The $ operator is different in that it get 4th result only takes element names as input, e.g. round table if your df was a dataframe with a column double chance values, df$values would subset that novel prc column. You can achieve the same [, but get mossier only with a quoted name such as off side back df["values"].

To answer more specifically, what does the changes df[[1]][] do? First, the [[-operator Nofile hosted will return the 1st element from df, and transparent text the following empty [-operator will pull Background movment everything from that output.