Date.MonthName

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The M Code Behind the Power Query M function Date.MonthName

But have you ever wondered how the Date.MonthName function actually works? In this article, we will take a deep dive into the M code behind the Date.MonthName function to understand how this powerful function is built.

The Basic Syntax

Before we dive into the code, let’s first take a look at the basic syntax of the Date.MonthName function. The syntax is as follows:

Date.MonthName(month as number, optional abbreviated as nullable logical, optional culture as nullable text) as text

The function takes three arguments:

- `month` (required): This is the numerical value of the month that you want to convert to a month name. This value must be between 1 and 12.

- `abbreviated` (optional): This argument is a logical value that determines whether you want the abbreviated or full month name. If this argument is set to `true`, then the abbreviated month name is returned. Otherwise, the full month name is returned. The default value is `false`.

- `culture` (optional): This argument is a text value that specifies the culture to use when converting the month name. If this argument is not provided, then the culture of the current user is used.

The M Code Behind the Function

Now let's take a look at the M code behind the Date.MonthName function. The M code is what actually makes the function work behind the scenes.

let

MonthNames = {“January”, “February”, “March”, “April”, “May”, “June”, “July”, “August”, “September”, “October”, “November”, “December”},

AbbreviatedMonthNames = {“Jan”, “Feb”, “Mar”, “Apr”, “May”, “Jun”, “Jul”, “Aug”, “Sep”, “Oct”, “Nov”, “Dec”},

MonthIndex = month – 1,

IsAbbreviated = if (abbreviated = null) then false else abbreviated,

Culture = if (culture = null) then #shared else culture,

MonthName = if (IsAbbreviated) then AbbreviatedMonthNames{MonthIndex} else MonthNames{MonthIndex},

Result = Text.Format(“{0}”, { MonthName })

in

Result

The M code above may look a bit intimidating if you are not familiar with it, but let's break it down step-by-step.

The first two lines of the code define two lists: `MonthNames` and `AbbreviatedMonthNames`. These lists contain the full and abbreviated month names, respectively.

The next line of the code calculates the index of the month in the `MonthNames` and `AbbreviatedMonthNames` lists. Since the lists are zero-based (i.e., the first element has an index of 0), we subtract 1 from the `month` argument to get the correct index.

The next two lines of code handle the optional arguments `abbreviated` and `culture`. If the `abbreviated` argument is not provided, then the variable `IsAbbreviated` is set to `false`. Otherwise, it is set to the value of the `abbreviated` argument. Similarly, if the `culture` argument is not provided, then the `Culture` variable is set to the current user's culture. Otherwise, it is set to the value of the `culture` argument.

The next line of the code uses the `IsAbbreviated` variable to determine whether to use the full or abbreviated month name. If `IsAbbreviated` is `true`, then the abbreviated month name is retrieved from the `AbbreviatedMonthNames` list and stored in the `MonthName` variable. Otherwise, the full month name is retrieved from the `MonthNames` list and stored in the `MonthName` variable.

The final line of the code uses the `Text.Format` function to format the `MonthName` variable as a string. The `{0}` in the format string represents the value of the `MonthName` variable.

In this article, we took a deep dive into the M code behind the Power Query M function Date.MonthName. We learned how the function works behind the scenes and how to use it with optional arguments. Armed with this knowledge, you can now use the Date.MonthName function with confidence in your Power Query projects.

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