# Order Months

Produce a vector of month names ending with the current month.

Jeremy Allen https://jeremydata.com
05-01-2020

## The last 12 months with order_months()

I frequently have to make tables or plots of events that “happened in the last 12 months.” I like to generate a character vector of month names for the last 12 months which I can then use for ordered factor levels, factor labels, column names, or x-axis labels.

This helper function will produce a character vector of names of the last 12 months ending either at the current month or a given month. The current month or given month will be the last element in the vector, with the preceding 11 months before it.

If no month number is given for x, the current month is used. Given months must be given as a number. Month names can be returned as abbreviated or full names. Set `label = "abb"` or `label = "names"`. X must be 1-12.

## Remember, the current or given month is always at the end of the vector!

``````
order_months <- function(x = NULL, label = "abb") {

# This function takes a given month number or the current month
# number and returns a character vector of the last 12 months,
# including current month. For example, if it is now February:
# "Mar" "Apr" "May" "Jun" "Jul" "Aug" "Sep" "Oct" "Nov" "Dec" "Jan" "Feb"
# is returned with the current month at the end.
# This makes a nice x axis if you need to plot something for
# the "last 12 months".
# if x is NULL the current month is taken from Sys.Date
# if x is given, x must be 1-12
# if label is "abb", month names are abbreviated
# if label is "names", month names are full

# stop if x is out of bounds
if(!is.null(x))
if(x > 12 | x < 1) stop("x must be 1-12")

# sets of named integers using abbreviated and full month names
months_abb <- setNames(1:12, month.abb)
months_names <- setNames(1:12, month.name)

# current month number
m <- as.POSIXlt(Sys.Date())\$mon + 1

# get a value for x
if(is.null(x)) x <- m + 1 else x <- x + 1

# a and b components for main if
# if x is 1 or 12
a <- 1:12
# if x is 2 through 12
b <- c(
x:12,
1:(x-1)
)

# main if
if(x == 1 | x == 13) new_order <- a else new_order <- b

# use new_order to set desired order of months
if(label == "abb") my_month_order <- names(months_abb[new_order])
if(label == "names") my_month_order <- names(months_names[new_order])

my_month_order
}``````

## Typical usage

``````
order_months()``````
``````
[1] "Jun" "Jul" "Aug" "Sep" "Oct" "Nov" "Dec" "Jan" "Feb" "Mar" "Apr"
[12] "May"``````
``````
order_months(label = "names")``````
``````
[1] "June"      "July"      "August"    "September" "October"
[6] "November"  "December"  "January"   "February"  "March"
[11] "April"     "May"      ``````
``````
order_months(x = 5, label = "abb")``````
``````
[1] "Jun" "Jul" "Aug" "Sep" "Oct" "Nov" "Dec" "Jan" "Feb" "Mar" "Apr"
[12] "May"``````

### Reuse

Text and figures are licensed under Creative Commons Attribution CC BY 4.0. The figures that have been reused from other sources don't fall under this license and can be recognized by a note in their caption: "Figure from ...".

### Citation

For attribution, please cite this work as

`Allen (2020, May 1). jeremydata: Order Months. Retrieved from https://jeremydata.com/posts/2020-05-01-order-months/`

BibTeX citation

```@misc{allen2020order,
author = {Allen, Jeremy},
title = {jeremydata: Order Months},
url = {https://jeremydata.com/posts/2020-05-01-order-months/},
year = {2020}
}```