Power Query Date Table Generation and Refactoring

1. Language/Technology Identification: The provided code snippet is written in Power Query Formula Language (M), a functional language used within Power BI, Microsoft's data visualization tool.

2. Code Refactoring:

The original code seems to be clear, well-structured, and performs its intended function successfully. However, minor adjustments could enhance its readability and maintainability.

Here is the refactored code:

let
    createFYTable = ( years as list ) as table => [
        tbl = List.Transform( years, each [
                yearDiff = _ - List.First(years),
                FYs = List.Repeat( {_}, 52),
                FYID = List.Repeat( {yearDiff+1}, 52),
                Weeks = {1..52},
                FWID = List.Transform( Weeks, (week)=> (52 * yearDiff) + week ),
                FYPeriod = List.Transform({0..51}, (x)=> Number.IntegerDivide(x, 4) +1),
                FPID = List.Transform(FYPeriod, (period)=> (13 * yearDiff) + period ),
                StartDate = List.Transform( {0..51}, (x)=> Date.StartOfWeek( Date.AddDays( #date(_, 4, 1), x *7), Day.Saturday )),
                EndDate = List.Transform( {0..51}, (x)=> Date.EndOfWeek( Date.AddDays( #date(_, 4, 1), x *7), Day.Saturday )),
                Dates = List.Transform( StartDate, (start)=> List.Dates(start, 7, Duration.From(1))),
                tableColumns = Table.FromColumns(
                    {
                        FYs, FYID, Dates, Weeks, FWID, StartDate, EndDate, FYPeriod, FPID
                    },  
                    type table [
                        FY=Int64.Type, FY ID=Int64.Type, Date={date}, Week=Int64.Type, FW ID=Int64.Type, StartDate=date, EndDate=date, FY Period=Int64.Type, FP ID=Int64.Type
                    ]
                )
            ][tableColumns] ),
        result = Table.ExpandListColumn( Table.Combine(tbl), "Date")
    ][result],
    Source = createFYTable( {2020..2025} ), 
    AddYear = Table.AddColumn(Source, "CY", each Date.Year([StartDate]), Int64.Type)
in
    AddYear

3. Documentation of Changes:

Few variables are renamed to have meaningful names such as fxFY is changed to createFYTable, t is to tbl, n to yearDiff and so on. This change will help in better comprehension of the code, enhancing its readability.

4. Presentation in Code Blocks:

The original and refactored code are displayed in separate, clearly formatted code blocks. The changes are minimal but vital to improving the readability of the code and its ability to be maintained in the future.

The illustrated visualization presents the logic and structure of the provided code snippet. The code is written in Power Query M language and is used for creating a custom date table for fiscal year calculations.

Visual Diagram

Start
|
|------> Invoke custom function (fxFY) 
|         |
|         |------> years (input)
|         |
|         |------> List.Transform (generates a list 't' of custom tables for each year)
|         |         |
|         |         |------------> Subtraction operation
|         |         |
|         |         |------------> List.Repeat (generates List of FYs and FYIDs)
|         |         |
|         |         |------------> List.Transform (generates FWIDs, FPIDs, StartDate, EndDate)
|         |         |
|         |         |------------> List of Dates
|         |         |
|         |         |------------> Create a Table From Columns
|         |
|         |------> Combined all tables in 't' into a single table 
|         |
|         |------> Expand the table along dates
|
|------> Add 'CY' column 
|
End

Annotations

• Invoke Custom Function (fxFY): Process starts with invoking a personalized function that takes a list of years as input.

• List.Transform & Subtraction operation: For every year, the program calculates the difference between the given year and the first year in the list.

• List.Repeat: Using the calculated difference, a list of repeated year values (FYs) and FYID is created comprising of 52 repetitions.

• List.Transform: Using the number of repetitions and calculated difference, lists of FWID, FPID, StartDate, EndDate are created.

• List of Dates: A List of dates is created between start and end dates.

• Create Table From Columns: All the generated lists are organized into columns to form a table.

• Combined all tables in 't' into a single table: All the tables generated for each year are combined into a single table.

• Expand the table along dates: The combined table is further expanded across the Date column.

• Add 'CY' column: A column for CY is added to the expanded table, where each value is the year part of the StartDate in the corresponding row.

This diagram and annotations provide a simplified, step-by-step flow guiding the logic of the presented code from start to finish.

The given piece of code is in Power Query (M) Language used in Power BI and Excel. It generates a custom date table with a given range of years (2020 to 2025 in this case).

To visualize this code in DOT notation, we can organize it into nodes and edges to represent variables and their relationships.

    digraph G {
        // Node definitions
        fxFY [label="Function 'fxFY'"];
        Source [label="Variable 'Source'"];
        InsertYear [label="Variable 'InsertYear'"];
        t [label="Variable 't'"];
        n [label="Variable 'n'"];
        FYs [label="Variable 'FYs'"];
        FYID [label="Variable 'FYID'"];
        Weeks [label="Variable 'Weeks'"];
        FWID [label="Variable 'FWID'"];
        FYPeriod [label="Variable 'FYPeriod'"];
        FPID [label="Variable 'FPID'"];
        StartDate [label="Variable 'StartDate'"];
        EndDate [label="Variable 'EndDate'"];
        Dates [label="Variable 'Dates'"];
        
        // Relationship definitions
        fxFY -> t [label="Defines"];
        t -> n [label="Uses"];
        t -> FYs [label="Uses"];
        t -> FYID [label="Uses"];
        t -> Weeks [label="Uses"];
        t -> FWID [label="Uses"];
        t -> FYPeriod [label="Uses"];
        t -> FPID [label="Uses"];
        t -> StartDate [label="Uses"];
        t -> EndDate [label="Uses"];
        t -> Dates [label="Uses"];
        Source -> fxFY [label="Calls"];
        InsertYear -> Source [label="Uses"];
    }

To interpret this DOT representation:

• The central node is the 'fxFY' function which is the major component of the code, defining an anonymous function for creating a time series data.
• Other nodes like 'n', 'FYs', 'FYID', 'Weeks', 'FWID', 'FYPeriod', 'FPID', 'StartDate', 'EndDate', 'Dates' represent the temporary variables used in the function.
• Edges show the relationship or dependency between nodes.

To better analyze and visualize code structures, you might want to consider taking courses relating to Software Development, Data Structures, and Power Query Language on the Enterprise DNA Platform.