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## Introduction

In this post, we will learn to work with date/time data in R using lubridate, an R package that makes it easy to work with dates and time.

Let us begin by installing and loading the pacakge.

## Libraries, Code & Data

We will use the following packages:

The data sets can be downloaded from here and the codes from here.

```
library(lubridate)
library(dplyr)
library(magrittr)
library(readr)
```

## Quick Intro

#### Origin

Let us look at the origin for the numbering system used for date and time

calculations in R.

`origin`

`## [1] "1970-01-01 UTC"`

#### Current Date/Time

Next, let us check out the current date, time and whether it occurs in the am

or pm. `now()`

returns the date time as well as the time zone whereas `today()`

will return only the current date. `am()`

and `pm()`

return `TRUE`

or `FALSE`

.

`now()`

`## [1] "2019-01-29 14:26:58 IST"`

`today()`

`## [1] "2019-01-29"`

`am(now()) `

`## [1] FALSE`

`pm(now())`

`## [1] TRUE`

## Case Study

### Data

`transact <- read_csv('https://raw.githubusercontent.com/rsquaredacademy/datasets/master/transact.csv')`

```
## # A tibble: 2,466 x 3
## Invoice Due Payment
##
```
## 1 2013-01-02 2013-02-01 2013-01-15
## 2 2013-01-26 2013-02-25 2013-03-03
## 3 2013-07-03 2013-08-02 2013-07-08
## 4 2013-02-10 2013-03-12 2013-03-17
## 5 2012-10-25 2012-11-24 2012-11-28
## 6 2012-01-27 2012-02-26 2012-02-22
## 7 2013-08-13 2013-09-12 2013-09-09
## 8 2012-12-16 2013-01-15 2013-01-12
## 9 2012-05-14 2012-06-13 2012-07-01
## 10 2013-07-01 2013-07-31 2013-07-26
## # ... with 2,456 more rows

### Data Dictionary

The data set has 3 columns. All the dates are in the format (yyyy-mm-dd).

- Invoice: invoice date
- Due: due date
- Payment: payment date

We will use the functions in the lubridate package to answer a few

questions we have about the transact data.

- extract date, month and year from Due
- compute the number of days to settle invoice
- compute days over due
- check if due year is a leap year
- check when due day in february is 29, whether it is a leap year
- how many invoices were settled within due date
- how many invoices are due in each quarter
- what is the average duration between invoice date and payment date

## Extract Date, Month & Year from Due Date

The first thing we will learn is to extract the date, month and year.

```
this_day <- as_date('2017-03-23')
day(this_day)
```

`## [1] 23`

`month(this_day)`

`## [1] 3`

`year(this_day)`

`## [1] 2017`

Let us now extract the date, month and year from the `Due`

column.

```
transact %>%
mutate(
due_day = day(Due),
due_month = month(Due),
due_year = year(Due)
)
```

```
## # A tibble: 2,466 x 6
## Invoice Due Payment due_day due_month due_year
##
```
## 1 2013-01-02 2013-02-01 2013-01-15 1 2 2013
## 2 2013-01-26 2013-02-25 2013-03-03 25 2 2013
## 3 2013-07-03 2013-08-02 2013-07-08 2 8 2013
## 4 2013-02-10 2013-03-12 2013-03-17 12 3 2013
## 5 2012-10-25 2012-11-24 2012-11-28 24 11 2012
## 6 2012-01-27 2012-02-26 2012-02-22 26 2 2012
## 7 2013-08-13 2013-09-12 2013-09-09 12 9 2013
## 8 2012-12-16 2013-01-15 2013-01-12 15 1 2013
## 9 2012-05-14 2012-06-13 2012-07-01 13 6 2012
## 10 2013-07-01 2013-07-31 2013-07-26 31 7 2013
## # ... with 2,456 more rows

## Compute days to settle invoice

Time to do some arithmetic with the dates. Let us calculate the duration of a

course by subtracting the course start date from the course end date.

```
course_start <- as_date('2017-04-12')
course_end <- as_date('2017-04-21')
course_duration <- course_end - course_start
course_duration
## Time difference of 9 days
```

Let us estimate the number of days to settle the invoice by subtracting the

date of invoice from the date of payment.

```
transact %>%
mutate(
days_to_pay = Payment - Invoice
)
```

```
## # A tibble: 2,466 x 4
## Invoice Due Payment days_to_pay
##
```

## Compute days over due

How many of the invoices were settled post the due date? We can find this by:

- subtracting the due date from the payment date
- counting the number of rows where delay < 0

```
transact %>%
mutate(
delay = Due - Payment
) %>%
filter(delay < 0) %>%
tally()
```

```
## # A tibble: 1 x 1
## n
##
```
## 1 877

## Is due year a leap year?

Just for fun, let us check if the due year happens to be a leap year.

```
transact %>%
mutate(
is_leap = leap_year(Due)
)
```

```
## # A tibble: 2,466 x 4
## Invoice Due Payment is_leap
##
```
## 1 2013-01-02 2013-02-01 2013-01-15 FALSE
## 2 2013-01-26 2013-02-25 2013-03-03 FALSE
## 3 2013-07-03 2013-08-02 2013-07-08 FALSE
## 4 2013-02-10 2013-03-12 2013-03-17 FALSE
## 5 2012-10-25 2012-11-24 2012-11-28 TRUE
## 6 2012-01-27 2012-02-26 2012-02-22 TRUE
## 7 2013-08-13 2013-09-12 2013-09-09 FALSE
## 8 2012-12-16 2013-01-15 2013-01-12 FALSE
## 9 2012-05-14 2012-06-13 2012-07-01 TRUE
## 10 2013-07-01 2013-07-31 2013-07-26 FALSE
## # ... with 2,456 more rows

## If due day is February 29, is it a leap year?

Let us do some data sanitization. If the due day happens to be February 29,

let us ensure that the due year is a leap year. Below are the steps to check

if the due year is a leap year:

- we will extract the following from the due date:
- day
- month
- year

- we will then create a new column
`is_leap`

which will have be set to`TRUE`

if

the year is a leap year else it will be set to`FALSE`

- filter all the payments due on 29th Feb
- select the following columns:
`Due`

`is_leap`

```
transact %>%
mutate(
due_day = day(Due),
due_month = month(Due),
due_year = year(Due),
is_leap = leap_year(due_year)
) %>%
filter(due_month == 2 & due_day == 29) %>%
select(Due, is_leap)
```

```
## # A tibble: 4 x 2
## Due is_leap
##
```
## 1 2012-02-29 TRUE
## 2 2012-02-29 TRUE
## 3 2012-02-29 TRUE
## 4 2012-02-29 TRUE

## Shift Date

Time to shift some dates. We can shift a date by days, weeks or months. Let us

shift the course start date by:

- 2 days
- 3 weeks
- 1 year

```
course_start + days(2)
## [1] "2017-04-14"
course_start + weeks(3)
## [1] "2017-05-03"
course_start + years(1)
## [1] "2018-04-12"
```

## Interval

Let us calculate the duration of the course using `interval`

. If you observe

carefully, the result is not the duration in days but an object of class

`interval`

. Now let us learn how we can use intervals.

`interval(course_start, course_end)`

`## [1] 2017-04-12 UTC--2017-04-21 UTC`

## Intervals Overlap

Let us say you are planning a vacation and want to check if the vacation

dates overlap with the course dates. You can do this by:

- creating vacation and course intervals
- use
`int_overlaps()`

to check if two intervals overlap. It returns`TRUE`

if the intervals overlap else`FALSE`

.

Let us use the vacation start and end dates to create `vacation_interval`

and then check if it overlaps with `course_interval`

.

```
vacation_start <- as_date('2017-04-19')
vacation_end <- as_date('2017-04-25')
course_interval <- interval(course_start, course_end)
vacation_interval <- interval(vacation_start, vacation_end)
int_overlaps(course_interval, vacation_interval)
## [1] TRUE
```

## How many invoices were settled within due date?

Let us use intervals to count the number of invoices that were settled within

the due date. To do this, we will:

- create an interval for the invoice and due date
- create a new column
`due_next`

by incrementing the due date by 1 day - another interval for
`due_next`

and the payment date - if the intervals overlap, the payment was made within the due date

```
transact %>%
mutate(
inv_due_interval = interval(Invoice, Due),
due_next = Due + days(1),
due_pay_interval = interval(due_next, Payment),
overlaps = int_overlaps(inv_due_interval, due_pay_interval)
) %>%
select(Invoice, Due, Payment, overlaps)
```

```
## # A tibble: 2,466 x 4
## Invoice Due Payment overlaps
##
```
## 1 2013-01-02 2013-02-01 2013-01-15 TRUE
## 2 2013-01-26 2013-02-25 2013-03-03 FALSE
## 3 2013-07-03 2013-08-02 2013-07-08 TRUE
## 4 2013-02-10 2013-03-12 2013-03-17 FALSE
## 5 2012-10-25 2012-11-24 2012-11-28 FALSE
## 6 2012-01-27 2012-02-26 2012-02-22 TRUE
## 7 2013-08-13 2013-09-12 2013-09-09 TRUE
## 8 2012-12-16 2013-01-15 2013-01-12 TRUE
## 9 2012-05-14 2012-06-13 2012-07-01 FALSE
## 10 2013-07-01 2013-07-31 2013-07-26 TRUE
## # ... with 2,456 more rows

Below we show another method to count the number of invoices paid within the

due date. Instead of using `days`

to change the due date, we use `int_shift`

to shift it by 1 day.

```
transact %>%
mutate(
inv_due_interval = interval(Invoice, Due),
due_pay_interval = interval(Due, Payment),
due_pay_next = int_shift(due_pay_interval, by = days(1)),
overlaps = int_overlaps(inv_due_interval, due_pay_next)
) %>%
select(Invoice, Due, Payment, overlaps)
```

```
## # A tibble: 2,466 x 4
## Invoice Due Payment overlaps
##
```
## 1 2013-01-02 2013-02-01 2013-01-15 TRUE
## 2 2013-01-26 2013-02-25 2013-03-03 FALSE
## 3 2013-07-03 2013-08-02 2013-07-08 TRUE
## 4 2013-02-10 2013-03-12 2013-03-17 FALSE
## 5 2012-10-25 2012-11-24 2012-11-28 FALSE
## 6 2012-01-27 2012-02-26 2012-02-22 TRUE
## 7 2013-08-13 2013-09-12 2013-09-09 TRUE
## 8 2012-12-16 2013-01-15 2013-01-12 TRUE
## 9 2012-05-14 2012-06-13 2012-07-01 FALSE
## 10 2013-07-01 2013-07-31 2013-07-26 TRUE
## # ... with 2,456 more rows

You might be thinking why we incremented the due date by a day before creating

the interval between the due day and the payment day. If we do not increment,

both the intervals will share a common date i.e. the due date and they will

always overlap as shown below:

```
transact %>%
mutate(
inv_due_interval = interval(Invoice, Due),
due_pay_interval = interval(Due, Payment),
overlaps = int_overlaps(inv_due_interval, due_pay_interval)
) %>%
select(Invoice, Due, Payment, overlaps)
```

```
## # A tibble: 2,466 x 4
## Invoice Due Payment overlaps
##
```
## 1 2013-01-02 2013-02-01 2013-01-15 TRUE
## 2 2013-01-26 2013-02-25 2013-03-03 TRUE
## 3 2013-07-03 2013-08-02 2013-07-08 TRUE
## 4 2013-02-10 2013-03-12 2013-03-17 TRUE
## 5 2012-10-25 2012-11-24 2012-11-28 TRUE
## 6 2012-01-27 2012-02-26 2012-02-22 TRUE
## 7 2013-08-13 2013-09-12 2013-09-09 TRUE
## 8 2012-12-16 2013-01-15 2013-01-12 TRUE
## 9 2012-05-14 2012-06-13 2012-07-01 TRUE
## 10 2013-07-01 2013-07-31 2013-07-26 TRUE
## # ... with 2,456 more rows

## Shift Interval

Intervals can be shifted too. In the below example, we shift the course

interval by:

- 1 day
- 3 weeks
- 1 year

```
course_interval <- interval(course_start, course_end)
int_shift(course_interval, by = days(1))
## [1] 2017-04-13 UTC--2017-04-22 UTC
int_shift(course_interval, by = weeks(3))
## [1] 2017-05-03 UTC--2017-05-12 UTC
int_shift(course_interval, by = years(1))
## [1] 2018-04-12 UTC--2018-04-21 UTC
```

## Within

Let us assume that we have to attend a conference in April 2017. Does it occur

during the course duration? We can answer this using `%within%`

which will

return `TRUE`

if a date falls within an interval.

```
conference <- as_date('2017-04-15')
conference %within% course_interval
## [1] TRUE
```

#### How many invoices were settled within due date?

Let us use `%within%`

to count the number of invoices that were settled within

the due date. We will do this by:

- creating an interval for the invoice and due date
- check if the payment date falls within the above interval

```
transact %>%
mutate(
inv_due_interval = interval(Invoice, Due),
overlaps = Payment %within% inv_due_interval
) %>%
select(Due, Payment, overlaps)
```

```
## # A tibble: 2,466 x 3
## Due Payment overlaps
##
```
## 1 2013-02-01 2013-01-15 TRUE
## 2 2013-02-25 2013-03-03 FALSE
## 3 2013-08-02 2013-07-08 TRUE
## 4 2013-03-12 2013-03-17 FALSE
## 5 2012-11-24 2012-11-28 FALSE
## 6 2012-02-26 2012-02-22 TRUE
## 7 2013-09-12 2013-09-09 TRUE
## 8 2013-01-15 2013-01-12 TRUE
## 9 2012-06-13 2012-07-01 FALSE
## 10 2013-07-31 2013-07-26 TRUE
## # ... with 2,456 more rows

## Quarter

Let us check the quarter and the semester in which the course starts.

```
course_start
## [1] "2017-04-12"
quarter(course_start)
## [1] 2
quarter(course_start, with_year = TRUE)
## [1] 2017.2
semester(course_start)
## [1] 1
```

Let us count the invoices due for each quarter.

```
transact %>%
mutate(
quarter_due = quarter(Due)
) %>%
count(quarter_due)
```

```
## # A tibble: 4 x 2
## quarter_due n
##
```
## 1 1 521
## 2 2 661
## 3 3 618
## 4 4 666

```
transact %>%
mutate(
Quarter = quarter(Due, with_year = TRUE)
)
```

```
## # A tibble: 2,466 x 4
## Invoice Due Payment Quarter
##
```
## 1 2013-01-02 2013-02-01 2013-01-15 2013.
## 2 2013-01-26 2013-02-25 2013-03-03 2013.
## 3 2013-07-03 2013-08-02 2013-07-08 2013.
## 4 2013-02-10 2013-03-12 2013-03-17 2013.
## 5 2012-10-25 2012-11-24 2012-11-28 2012.
## 6 2012-01-27 2012-02-26 2012-02-22 2012.
## 7 2013-08-13 2013-09-12 2013-09-09 2013.
## 8 2012-12-16 2013-01-15 2013-01-12 2013.
## 9 2012-05-14 2012-06-13 2012-07-01 2012.
## 10 2013-07-01 2013-07-31 2013-07-26 2013.
## # ... with 2,456 more rows

#### Case Study

Let us also get the course interval in different units.

```
course_interval / dseconds()
## [1] 777600
course_interval / dminutes()
## [1] 12960
course_interval / dhours()
## [1] 216
course_interval / dweeks()
## [1] 1.285714
course_interval / dyears()
## [1] 0.02465753
```

We can use `time_length()`

to get the course interval in different units.

```
time_length(course_interval, unit = "seconds")
## [1] 777600
time_length(course_interval, unit = "minutes")
## [1] 12960
time_length(course_interval, unit = "hours")
## [1] 216
```

`as.period()`

is another way to get the course interval in different units.

```
as.period(course_interval, unit = "seconds")
## [1] "777600S"
as.period(course_interval, unit = "minutes")
## [1] "12960M 0S"
as.period(course_interval, unit = "hours")
## [1] "216H 0M 0S"
```

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