R07_lists.qmd

# Lists

- stores arbitrary content (string, numeric, vectors...)
- created with `list()`, entries separated by `,`


```{r}
number = 6
l = list(5, number, "Gardenia", c(1,5))
l
```


## Some generic functions with lists

```{r}
length(l)

summary(l)
```


## Subsetting Lists


There are multiple ways to subset a list (i.e. get a specific or multiple entries).

Subsetting with `[ ]` returns a list.
```{r}
l[1]
class(l[1])


# We can select multiple entries by using a vector
l[c(1,3)]
```


More commonly you don't want a list, but the content that is stored in the list.
For this you use double square brackets `[[ ]]`.


```{r}
#| error: true

l[[2]]
class(l[[2]])


# Selecting multiple entries like this is not possible

l[[c(1,2)]]
```


## Named entries

Lists become even more useful when we start to name list entries.
Our created list does not have names (we declared no names in the list creation).


```{r}
names(l)
names(l) = c("a", "b", "c", "d")
l
```

Calling the list now also shows the entry names (after the `$`).
We can use the names now to select specific entries.

```{r}

# single brackets: return list
l[c("c", "a")]

# double brackets: return value
l[["b"]]
# or use the dollar sign $
l$b
```