Parse Ethiopian Dates • ethiodate

Introduction

The Ethiopian calendar is widely used in Ethiopia and differs significantly from the Gregorian calendar. It has 13 months: 12 months of 30 days and a 13th month (Pagumē) of 5 or 6 days, depending on the year.

The ethiodate package provides tools for parsing, converting, and working with Ethiopian dates in R. This vignette demonstrates how to parse Ethiopian dates from strings or numeric formats and convert them into ethdate objects.

Parsing Ethiopian Dates

From Character Strings

You can parse Ethiopian dates from standard character representations like “2015-01-01” (Ethiopian calendar). Use eth_parse_date():

library(ethiodate)
eth_parse_date("2015-01-01")
#> [1] "2015-01-01"

You can also provide a vector of dates:

eth_dates <- c("2015-01-01", "2015-02-15", "2015-13-05")
eth_parse_date(eth_dates)
#> [1] "2015-01-01" "2015-02-15" "2015-13-05"

If you are parsing dates from string, you must provide correct formatting using format argument and the string must have consistent pattern. This argument accepts ISO 8601 formats, use ?strptime for more.

Examples

x <- c("01/17/2025", "05/12/2017")
eth_parse_date(x, format = "%m/%d/%Y")
#> [1] "2025-01-17" "2017-05-12"

You can also parse date that contains month names if specify the exact format as follows:

eth_parse_date("Meskerem 25, 2017", format = "%B %d, %Y")
#> [1] "2017-01-25"
eth_parse_date("መስከረም 25, 2017", format = "%B %d, %Y", lang = "amh")
#> [1] "2017-01-25"
eth_parse_date("Sep 25, 2017", format = "%b %d, %Y", lang = "en")
#> [1] "2017-01-25"

From Numeric

ethate is just a numeric vector, under the hood, representing number of days since 1970-01-01 GC (1962-04-12 EC). The date before the origin is represented by negative values. This makes it to seamlessly integrate features if base R Date object. For instance;

# The same origin
eth_parse_date("1962-04-23") |> unclass()
#> [1] 0
as.Date("1970-01-01") |> unclass()
#> [1] 0

So, you can supply number of days from a custom origin to construct Ethiopian date object. If the origin is missing, the default is 1962-04-23 EC. See ?eth_date for more.

eth_date(7, origin = eth_today())
#> [1] "2017-09-05"

From Components

Constructing ethdate object from separate vector of year, month and day is supported.

eth_make_date(2017, 1, 1)
#> [1] "2017-01-01"

y <- c(2022, 2025)
m <- c(5, 9)
d <- c(15, 19)
eth_make_date(y, m, d)
#> [1] "2022-05-15" "2025-09-19"

Invalid and Missing Values

ethiodate validates every values before coercing it to ethdate object. For instance, 13th month has 6 days only during leap year. If you supply such erroneous values, you will NA's along with warnig message.

# 2011 is leap year -> Correct
eth_date("2011-13-6")
#> [1] "2011-13-06"

# Incorrect
eth_date("2012-13-6")
#> Warning in eth_date_validate(year = year, month = month, day = day): Detected 1
#> invalid date and coerced to NA.
#> [1] NA

Conversion

Conversion between Ethiopian and Gregorian calendar is fully supported.

To Ethiopian

gre_date <- as.Date("2025-01-15")
eth_date(gre_date)
#> [1] "2017-05-07"

To Gregorian

eth_dt <- eth_date(0)
as.Date(eth_dt)
#> [1] "1970-01-01"

Operations

As any other date objects, ethdate supports date operations. A unit any arithmetric operations is date.

# Adding scalar days
eth_date("2010-09-14") + 6
#> [1] "2010-09-20"

# Subtraction
eth_date("2010-09-14") - 6
#> [1] "2010-09-08"

# Differences
eth_date("2010-09-14") - eth_date("2010-09-10")
#> [1] "Time difference of 4 days"

Formatting

You can format ethdate object like any other date objects.

format(eth_today(), format = "This documents was updated on %B %d, %Y EC.")
#> [1] "This documents was updated on Miyazya 28, 2017 EC."

Conclusion

Parsing Ethiopian dates is a crucial step in analyzing data collected in the Ethiopian calendar system. The ethiodate package provides a consistent and robust interface for converting string representations of Ethiopian dates into properly classed objects ready for further analysis or conversion.

For more functionality, see ?eth_date, ?eth_parse_date, ?eth_make_date, and the rest of the package documentation.