Can I parameterize the Table.ReplaceValue command in a custom function?

[olimilo]

I made the custom function below as I need to run the same function for 15+ columns, basically to replace colA with colB if it isn't null, otherwise to retain the value of colA:

let updateField = (dt as table, colA as text, colB as text) =>
    let Source =
        Table.ReplaceValue(dt, each colA, each if colB <> null then colB else colA, Replacer.ReplaceValue, {colA})
    in Source
in updateField

Unfortunately, when I invoked the custom function in my query, it didn't work. However, if I use the actual Table.ReplaceValue in a step, it works just fine. Is there some way I can make this function work? I figure what's causing it is because colA and colB are text parameters, but I don't think I can pass a column as a parameter.

[LillyBeast]

You would need to wrap that in an Evaluate.Expression to allow running text as M-Code. See this example 
Also, Table.ReplaceValue is really just passing (in_value, look_for, replace_with) parameters to any function. You could write yours as:

Table.ReplaceValue(
   table
   , each _ColA
   , each _ColB
   , (value, old, new) => old ?? new
   , {ColA}
)

The `??` operator is M-Code's null-coalesce

[LillyBeast]

It needs an Evaluate.Expression wrap to allow running text as M-Code. See this example 
Also, Table.ReplaceValue is simply passing three arguments - (in_value, look_for, replace_with) - to any function. Replacer.ReplaceValue is just a function that is used in the documentation, without really explaining how that works.
So, try this:

Evaluate.Expression(
   "Table.ReplaceValue(
      table
      , each _" & ColA & "
      , each _" & ColB & "
      , (value, value_in_ColA, value_in_ColB) => value_in_ColA ?? value_in_ColB
      , {" & ColA & "}
   )"
   ,[Table.ReplaceValue = Table.ReplaceValue]
)

* -  `??` operator is M-Code's null-coalesce

[v-lionel-msft]

Hi @olimilo ,

I think you need to reference the Table.ReplaceValue() function once for each column you want to replace.

Best regards,
Lionel Chen

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