- A vector can be thought as contiguous cells containing elemental data.

Indexing: x[i], x[i,j]

Concatenating vectors x <- c(x,x)

- A list (generic vector) has elements, each of which can contain any type of R object.

`name_1`=

`object_1`,

`...`,

`name_m`=

`object_m`)

Indexing: x[[i]], x[[i,j]], x$a, x$"a", x[["a"]]

Concatenating lists: list.ABC <- c(list.A, list.B, list.C)

- A
*data frame*is a list with class`"data.frame"`

. There are restrictions: - The components must be vectors (numeric, character, or logical), factors, numeric matrices, lists, or other data frames.
- Matrices, lists, and data frames provide as many variables to the new data frame as they have columns, elements, or variables, respectively.
- Numeric vectors, logicals and factors are included as is, and character vectors are coerced to be factors, whose levels are the unique values appearing in the vector.
- Vector structures appearing as variables of the data frame must all have the
*same length*, and matrix structures must all have the same*row size*.

Attach and dettach:

(For lists in general). A useful facility would be somehow to make the components of a list or data frame temporarily visible as variables under their component name, without the need to quote the list name explicitly each time.The `attach()`

function takes a `database' such as a list or data frame as its argument.