A `number_line`

object is a range of `numeric`

values. `number_line`

objects as based off
`interval`

objects from the `lubridate`

package
but supports any object that can be successfully coerced to a
`numeric`

object.

For a given `number_line`

object
e.g. `8 <- 1`

, its main components are;

`left_point()`

- left side of the`number_line`

`i.e.`

`8`

`right_point()`

- right side of the`number_line`

`i.e.`

`1`

`start_point()`

- lower end of the range`i.e.`

`1`

`end_point()`

- upper end of the range`i.e.`

`8`

`direction`

-`"decreasing"`

`(<-)`

,`"increasing"`

`(->)`

or no direction`(==)`

`number_line_width()`

- difference between the left and right points`i.e.`

`-7`

For an `"increasing"`

`number_line`

, its
`start_point()`

is at the `left_point()`

. In
contrast, the `start_point()`

of a `"decreasing"`

`number_line`

is at the `right_point()`

.

```
library(diyar)
# `number_line` objects
<- number_line(l = c(3, 5), r = c(4, 1))
nl_a
nl_a#> [1] "3 -> 4" "5 <- 1"
# Lower end of the range
start_point(nl_a)
#> [1] 3 1
# Left part of the range
left_point(nl_a)
#> [1] 3 5
```

`number_line`

There are convenience functions to reverse, shrink, expand or shift a
`number_line`

along the number line.

```
<- number_line(as.Date("2019-04-04"), as.Date("2019-4-07"))
nl_c
nl_c#> [1] "2019-04-04 -> 2019-04-07"
# Expand the `number_line` by 2 days from both ends
<- expand_number_line(nl_c, 2); nl_d
nl_d #> [1] "2019-04-02 -> 2019-04-09"
# Expand the `number_line` by 2 days from the lower end only
<- expand_number_line(nl_c, 2, "start"); nl_e
nl_e #> [1] "2019-04-02 -> 2019-04-07"
# Shrink the `number_line` by 2 days from the upper end only
<- expand_number_line(nl_c, -2, "end"); nl_f
nl_f #> [1] "2019-04-04 -> 2019-04-05"
# Shrink the `number_line` by 2 days from both ends
<- expand_number_line(nl_c, -2); nl_g
nl_g #> [1] "2019-04-06 <- 2019-04-05"
# Reverse the direction of the `number_line`
<- reverse_number_line(nl_c); nl_h
nl_h #> [1] "2019-04-07 <- 2019-04-04"
# Shift the `number_line` towards the negative end of the number line by 2 days
<- shift_number_line(nl_c, -2); nl_i
nl_i #> [1] "2019-04-02 -> 2019-04-05"
# Shift the `number_line` towards the positive end of the number line by 2 days
<- shift_number_line(nl_c, 2); nl_j
nl_j #> [1] "2019-04-06 -> 2019-04-09"
# Change the left part of the `number_line` to a negative value
<- invert_number_line(nl_c, "left"); nl_k
nl_k #> [1] "-17990 -> 17993"
# Split a `number_line`
<- seq(nl_c, length.out = 3); nl_l
nl_l #> [1] "2019-04-04 -> 2019-04-05" "2019-04-05 -> 2019-04-07"
```

`number_line`

objects can overlap with each other.
`diyar`

recognises seven ways this can happen. These are
`exact()`

, `inbetween()`

, `across()`

,
`chain()`

, `aligns_start()`

and
`aligns_end()`

. The 6 methods are mutually exclusive. There
are 2 convenience methods - `"none"`

and
`overlap()`

, which are mutually inclusive with the other 6.
See Figure 1.

**Figure 1: Overlap methods for
number_line**

```
<- c(number_line(1, 5), number_line(1, 5), number_line(5, 9))
nl_1 <- c(number_line(1, 2), number_line(2, 7), number_line(0, 6))
nl_2
# Union
union_number_lines(nl_1, nl_2)
nl_1; nl_2; #> [1] "1 -> 5" "1 -> 5" "5 -> 9"
#> [1] "1 -> 2" "2 -> 7" "0 -> 6"
#> [1] "1 -> 5" "1 -> 7" "0 -> 9"
<- number_line(as.Date(c("01/01/2020", "03/01/2020","09/01/2020"), "%d/%m/%Y"),
nl_3 as.Date(c("09/01/2020", "09/01/2020","25/12/2020"), "%d/%m/%Y"))
<- number_line(as.Date(c("04/01/2020","01/01/2020","01/01/2020"), "%d/%m/%Y"),
nl_4 as.Date(c("05/01/2020","05/01/2020","03/01/2020"), "%d/%m/%Y"))
# Intersect
intersect_number_lines(nl_3, nl_4)
nl_3; nl_4; #> [1] "2020-01-01 -> 2020-01-09" "2020-01-03 -> 2020-01-09"
#> [3] "2020-01-09 -> 2020-12-25"
#> [1] "2020-01-04 -> 2020-01-05" "2020-01-01 -> 2020-01-05"
#> [3] "2020-01-01 -> 2020-01-03"
#> [1] "2020-01-04 -> 2020-01-05" "2020-01-03 -> 2020-01-05"
#> [3] "NA ?? NA"
# Subtract
subtract_number_lines(nl_3, nl_4)
nl_3; nl_4; #> [1] "2020-01-01 -> 2020-01-09" "2020-01-03 -> 2020-01-09"
#> [3] "2020-01-09 -> 2020-12-25"
#> [1] "2020-01-04 -> 2020-01-05" "2020-01-01 -> 2020-01-05"
#> [3] "2020-01-01 -> 2020-01-03"
#> $n1
#> [1] "2020-01-01 -> 2020-01-04" "2020-01-01 -> 2020-01-03"
#> [3] "NA ?? NA"
#>
#> $n2
#> [1] "2020-01-05 -> 2020-01-09" "2020-01-05 -> 2020-01-09"
#> [3] "NA ?? NA"
```