I have a data table containing ids with a start date and end date associated with both.
RowNo AcNo StartDate EndDate
1 R125 01/10/2017
Only because you seem to be soliciting multiple options, here is one without VBA:
=IF(EOMONTH(Table1[@[StartDate]:[StartDate]],COLUMNS($A:A))
Power Query or Data Get & Transform to unPivot all except the first two columns: (easily done in the GUI, but I paste the code below for interest)let
Source = Excel.CurrentWorkbook(){[Name="Table1"]}[Content],
#"Changed Type" = Table.TransformColumnTypes(Source,{{"RowNo", Int64.Type}, {"AcNo", type text}, {"StartDate", type datetime}, {"EndDate", type datetime}, {"Column1", type datetime}, {"Column2", type datetime}, {"Column3", type datetime}, {"Column4", type datetime}, {"Column5", type datetime}, {"Column6", type datetime}, {"Column7", type datetime}, {"Column8", type datetime}, {"Column9", type datetime}, {"Column10", type datetime}, {"Column11", type datetime}, {"Column12", type datetime}, {"Column13", type datetime}, {"Column14", type datetime}, {"Column15", type datetime}, {"Column16", type datetime}, {"Column17", type datetime}, {"Column18", type datetime}, {"Column19", type datetime}, {"Column20", type datetime}, {"Column21", type datetime}, {"Column22", type datetime}, {"Column23", type datetime}, {"Column24", type datetime}, {"Column25", type datetime}, {"Column26", type datetime}, {"Column27", type datetime}, {"Column28", type datetime}, {"Column29", type datetime}, {"Column30", type datetime}, {"Column31", type datetime}, {"Column32", type datetime}, {"Column33", type datetime}, {"Column34", type datetime}}),
#"Unpivoted Other Columns" = Table.UnpivotOtherColumns(#"Changed Type", {"RowNo", "AcNo"}, "Attribute", "Value"),
#"Removed Columns" = Table.RemoveColumns(#"Unpivoted Other Columns",{"Attribute"}),
#"Renamed Columns" = Table.RenameColumns(#"Removed Columns",{{"Value", "EOM Date"}}),
#"Changed Type1" = Table.TransformColumnTypes(#"Renamed Columns",{{"EOM Date", type date}})
in
#"Changed Type1"
Note that, when done this way, the first date is actually a BOM date, but if you format them as in your results, mmm yy, it'll look the same. And things are easily changed if that is an issue.
If having the first month as a BOM date is not desired:
=IF(EOMONTH(Table1[@[StartDate]:[StartDate]],COLUMNS($A:A)-1)<=Table1[@[EndDate]:[EndDate]],EOMONTH(Table1[@[StartDate]:[StartDate]],COLUMNS($A:A)-1),"")
Data Get & Transform, delete the StartDate column in the Query GUI editor, as this will not affect the other columns at that time.