Forum Discussion
Syntax for Looping through a List in an M function
Hi pelowski ,
My understanding was you just wanted to loop through each item in a list but not create tables out of it. The screenshot would have helped 😊. Anyway, the custom function below creates a table of name of day based on a list of cultures. I didn't use List.Accumulate as this could be slow if used on a large dataset.
let fnAddCultures = ( date as date, Cultures as list ) as table=> let list = List.Transform ( Cultures, each Date.DayOfWeekName ( date, _ ) ), table = Table.FromList(list, null), transpose = Table.Transpose(table), newname = List.Zip({Table.ColumnNames(transpose), Cultures}) in Table.RenameColumns(transpose, newname) in fnAddCulturesAnd here's a sample table generated from a list of dates and the custom function
let Dates = Table.FromList(List.Dates(#date(2010, 1, 1 ), 365.25 * 25, #duration(1,0,0,0)), Splitter.SplitByNothing(), {"Dates"}, null, ExtraValues.Error), #"Invoked Custom Function" = Table.AddColumn(Dates, "Day Name in Culture", each fnAddCultures([Dates], Cultures[Column1])), #"Expanded Day Name in Culture" = Table.ExpandTableColumn(#"Invoked Custom Function", "Day Name in Culture", {"en-US", "de-DE", "fr-FR", "pl-PL", "ru-RU", "es-ES", "zh-HK"}, {"en-US", "de-DE", "fr-FR", "pl-PL", "ru-RU", "es-ES", "zh-HK"}) in #"Expanded Day Name in Culture"
danextian, I don't understand what you're suggesting. The problem becomes the same but from a different list's point of view. I understand how to do a List.Transform, but I don't understand how to execute a looping construct over a list for a custom function I've written. With the code you provided, now looping through the Dates list becomes the task but the problem is the same for me. How do I execute a looping construct over the List?
What I'm trying to achieve in an example like this is the following...
I'm trying to follow Ben Gribaudo's example here, but I wish I could see how the function he wrote gets executed to better understand how the looping works.
To put this in a slightly different way, I'm trying to loop over one object in the context of another. In this case, I'm trying to loop through what amounts to two lists in the context of a table in order to add a column for each item in a list and a row for each value in another list. I've done plenty of for/each and do/until loops in other languages but the syntax of doing this in Power Query is tripping me up.