> For the complete documentation index, see [llms.txt](https://r-pedia.gitbook.io/cevi/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://r-pedia.gitbook.io/cevi/r-programming-track/a-introduction-to-r/6-lists.md).

# --6-Lists

\#1-Lists, why would you need them?

```r
#Within a column all elements have the same data type,
#but different columns can be of different data type.
```

\#2-Lists, why would you need them? (2)

```r
#A list in R allows you to gather a variety of 
#objects under one name 
#(that is, the name of the list) in an ordered way. 
#These objects can be matrices, vectors, data frames, 
#even other lists, etc. 
#It is not even required that these objects are related 
#to each other 
#in any way
```

 \#3-Creating a list

```r
#Construct a list, named my_list, that contains 
#the variables my_vector, 
#my_matrix and my_df as list components.

# Vector with numerics from 1 up to 10
my_vector <- 1:10 

# Matrix with numerics from 1 up to 9
my_matrix <- matrix(1:9, ncol = 3)

# First 10 elements of the built-in data frame mtcars
my_df <- mtcars[1:10,]

# Construct list with these different elements:
my_list <- list(my_vector,my_matrix,my_df)
my_list
```

\#4-Creating a named list

\#Change the code of the previous exercise (see editor) by adding names to the components. Use for #`my_vector` the name `vec`, for `my_matrix` the name `mat` and for `my_df` the name `df`.

\#Print out `my_list` so you can inspect the output.

```r
# Vector with numerics from 1 up to 10
my_vector <- 1:10 

# Matrix with numerics from 1 up to 9
my_matrix <- matrix(1:9, ncol = 3)

# First 10 elements of the built-in data frame mtcars
my_df <- mtcars[1:10,]

# Adapt list() call to give the components names
my_list <- list(my_vector, my_matrix, my_df)
names(my_list)<-c("vec","mat","df")

# Print out my_list
my_list
```

5-Creating a named list (2)

Complete the code on the right to create `shining_list`; it contains three elements:

* moviename: a character string with the movie title (stored in `mov`)
* actors: a vector with the main actors' names (stored in `act`)
* reviews: a data frame that contains some reviews (stored in `rev`)

Do not forget to name the list components accordingly (names are moviename, actors and reviews).

```r
# The variables mov, act and rev are available:
mov<-c("The Shining")
act<-c("Jack Nicholson", "Shelley Duvall","Danny Lloyd")
rev<-c("good","bad")

# Finish the code to build shining_list
shining_list <- list(moviename = mov,actors=act,reviews=rev)
shining_list
```

\#6-Selecting elements from a list

* Select from `shining_list` the vector representing the actors. Simply print out this vector.
* Select from `shining_list` the second element in the vector representing the actors. Do a printout like before.

```r
# shining_list is already pre-loaded in the workspace
# The variables mov, act and rev are available:
mov<-c("The Shining")
act<-c("Jack Nicholson", "Shelley Duvall","Danny Lloyd")
rev<-c("good","bad")

# Finish the code to build shining_list
shining_list <- list(moviename = mov,actors=act,reviews=rev)
shining_list

# Print out the vector representing the actors
shining_list$actors

# Print the second element of the vector representing 
#the actors
shining_list[[2]][2]

shining_list[[2]][3]# in second list element no 3
```

\#7-Adding more movie information to the list

* Complete the code below such that an item named `year` is added to the `shining_list` with the value 1980. Assign the result to `shining_list_full`.
* Finally, have a look at the structure of `shining_list_full` with the [`str()`](http://www.rdocumentation.org/packages/utils/functions/str) function.

```r
# shining_list, the list containing movie name, 
#actors and reviews, 
#is pre-loaded in the workspace:
mov<-c("The Shining")
act<-c("Jack Nicholson", "Shelley Duvall","Danny Lloyd")
rev<-c("good","bad")

# Finish the code to build shining_list
shining_list <- list(moviename = mov,actors=act,reviews=rev)
shining_list

# Print out the vector representing the actors
shining_list$actors

# Print the second element of the vector representing 
#the actors
shining_list[[2]][2]

shining_list[[2]][3]# in second list element no 3

# We forgot something; add the year to shining_list
shining_list_full <- c(shining_list,year=1980)

# Have a look at shining_list_full
str(shining_list_full)
shining_list_full
```