M formula to check if text is a number and avoid errors

Hi Lucian 

It may not be the optimum solution but you can add intermediate steps:

1. Add a try to Number.FromText and write "Not number" if error

2. Then, create a conditional formula (if column = "Not number" then "Not number" else "Is number")

3. Remove extra columns not needed

let
    Origen = Excel.Workbook(File.Contents("C:\ex.xlsx"), null, true),
    Hoja1_Sheet = Origen{[Item="Sheet",Kind="Sheet"]}[Data],
    #"Encabezados promovidos" = Table.PromoteHeaders(Hoja1_Sheet, [PromoteAllScalars=true]),
    #"Tipo cambiado" = Table.TransformColumnTypes(#"Encabezados promovidos",{{"TestColumn", type text}}),
    #"Primeros caracteres insertados" = Table.AddColumn(#"Tipo cambiado", "Primeros caracteres", each Text.Start([TestColumn], 4), type text),
    #"Columnas con nombre cambiado" = Table.RenameColumns(#"Primeros caracteres insertados",{{"Primeros caracteres", "FirstChar"}}),
    #"Personalizada agregada" = Table.AddColumn(#"Columnas con nombre cambiado", "IsNumber", each try Number.FromText([FirstChar]) otherwise "Not Number"),
    #"Columna condicional agregada" = Table.AddColumn(#"Personalizada agregada", "isNumb", each if [IsNumber] <> "Not Number" then "Is Number" else "Not Number"),
    #"Columnas quitadas" = Table.RemoveColumns(#"Columna condicional agregada",{"FirstChar", "IsNumber"})
in
    #"Columnas quitadas"