Create Custom Functin CountMonths.pq (#12)

Custom function to count the number of months between two dates

Functions/Date/CountMonths.pq

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+let pq_custom_function =
+
+let
+    // Define metadata for the function, describing its purpose and usage.
+    metaDocumentation = type function (
+        StartDate as (type date meta [
+            Documentation.FieldCaption = "Start Date",
+            Documentation.SampleValues = {" 01/01/2024 (dd/MM/yyyy) "},
+            // Documentation.AllowedValues = {"01/01/2024"},
+            Formatting.IsMultiLine = false,
+            Formatting.IsCode = false
+        ]),
+        EndDate as (type date meta [
+            Documentation.FieldCaption = "End Date",
+            Documentation.SampleValues = {" 31/01/2024 (dd/MM/yyyy) "},
+            // Documentation.AllowedValues = {"31/01/2025"},
+            Formatting.IsMultiLine = false,
+            Formatting.IsCode = false
+        ]),
+        optional CompletedMonthsOnly as (type nullable logical meta [
+            Documentation.FieldCaption = "Do you want to count completed months only?",
+            Documentation.FieldDescription = "Count by completed months (true) or actual months (false)",
+            Documentation.SampleValues = {"True", "False"},
+            Documentation.AllowedValues = {true,false},
+            Formatting.IsMultiLine = false,
+            Formatting.IsCode = true
+        ])
+    ) as list meta [
+        Documentation.Name = "fnCountMonths",
+
+        Documentation.LongDescription = 
+        "    
+                <p><b>  Count Months Between Dates  </b></p>
+
+                <li>------------------------------------------------------</li>
+
+                <li><b>  Creator: </b> Imran Haq  </li>
+                <li><b>  Web: </b> https://github.com/PBIQueryous  </li>
+                <li><b>  Acknowledgements: </b>   </li>
+                <li><b>  LinkedIn: </b>   </li>
+
+                <li>------------------------------------------------------</li>
+
+                <li><b>  Editor: </b>  Oscar Martinez  </li>
+                <li><b>  Web: </b>  https://bibb.pro  </li>
+                <li><b>  LinkedIn: </b>  https://www.linkedin.com/in/oscarmartinezv/  </li>
+
+                <li>------------------------------------------------------</li>
+
+                <p><b>  Function Description:  </b></br>
+                This function counts the number of months between the a selected Start Date and End Date. The third parameter allow you to count either complete months or actual months
+
+                <p><b>  Parameters:  </b></br>
+                <ul>
+                    <li><b>  • StartDate:  </b>  The Start Date field from your data. <code> (eg: 01/01/2024) </code> </li>
+                    <li><b>  • EndDate:  </b>  The End Date field from your data. <code> (eg: 31/12/2025) </code> </li>
+                    <li><b>  • CompletedMonthsOnly:  </b>  Select 'true' to count only completed months, 'false' for actual months. </li>
+
+                </ul>
+
+                <b>  Returns:  </b></br>
+                A custom column.
+
+                <p><b>  formula bar (fx) example:  </b></br>
+                <code>  fn_CountMonths( [StartDate], [EndDate], true )  </code>
+
+            "
+    ],
+    // Define the main function
+
+myFunction = (StartDate as date, EndDate as date, optional CompletedMonthsOnly as nullable logical) =>
+
+  let invoke_custom_function =
+// paste your custom function here
+// _______________________________
+        let
+          countWholeMonths = if (CompletedMonthsOnly ?? true) = true then -1 else 0, 
+          MonthsList = List.Generate(
+            () => [DateValue = Date.From(StartDate)], 
+            each Date.From([DateValue]) <= Date.AddDays(Date.StartOfMonth(Date.From(EndDate)), countWholeMonths), 
+            each [DateValue = Date.AddMonths([DateValue], 1)], 
+            each Date.From([DateValue])
+          ), 
+          MonthsCount = Int64.From(List.Count(MonthsList))
+        in
+          MonthsCount
+// _______________________________
+  in invoke_custom_function,
+
+    replaceMetaData = Value.ReplaceType(myFunction, metaDocumentation)
+
+  in
+    replaceMetaData
+in
+  pq_custom_function