Power Query - Table.ReplaceValue - Behavior ?

It might help to look closely at Example 4 in the MS documentation for Table.ReplaceValue

And what might be confusing is that, although Table.ReplaceValue passes 3 values to the fourth argument, they are not passed "in order".

Rather, if we use (x,y,z)

The fact that three parameters are passed to the 4th argument is implied by Example 4, and also by the Replacer function which has three non-optional parameters.

"What is assigned to them" can also be seen in the fourth example, where it is clear that the first parameter corresponds to the 5th argument, the second to the second, and the third to the third argument of the Table.ReplaceValue function. (Sometimes it is not so clear).

It is not laid out in more detail because it is part of the architecture of how the M language works, and you'd have to delve deeply into the architecture and specifications to better understand that. Power Query M formula language 

Stéphane,
Le voile de l'incompréhension se lève doucement grâce à vous et à toute la communauté toutefois je trouve que la documentation sur M qui est disponible sur MSN et internet en général est parcellaire, lacunaire et peu explicite !

Par exemple pour Table.ReplaceValue, la documentation se résume à une définition

Table.ReplaceValue(
   table as table,
   oldValue as any,
   newValue as any,
   replacer as function,
   columnsToSearch as list,
) as table

Et comment deduire de

replacer function

Qu'une fonction personnalisée doit obligatoirement passer 3 paramètres alors que si on appelle les 2 fonctions ci-dessous, aucun paramètre n'est demandé ?

Replacer.ReplaceValue et Replacer.ReplaceText

Exemple

= Table.ReplaceValue(#table( {"text", "Col1", "Col2"}, { {"azeurty",1, 2}, {"azeurty",3, 4} } ),
"ur", "", Replacer.ReplaceText, {"text"})

 output
text Col1 Col2
azety 1 2
azety 3 4

Et comment déduire que si une fonction personnelle est implémentée, en plus de devoir passer 3 paramètres ( x,y,z) => ,

x = Source

y = oldValue

z = NewValue

Sauf s'il existe une documentation qui l'explique mais je n'ai jamais reussi à accéder à cette information. Ou alors j'ai vraiment raté plus qu'une marche !!!

Ah, so you haven't played with List.Accumulate  yet?  or with this one?  Table.Group: Exploring the 5th element in Power BI and Power Query –

Hi  ronrsnfld,

Thanks for yoour help

For each step forward, I take at least 2 steps back
Take a look at the page Learn microsoft - powerquery M - Table.Replacevalue he definition of the function is

Table.ReplaceValue(table as table, oldValue as any, newValue as any, replacer as function, columnsToSearch as list) as table

I modifyed the 4th example as below

= Table.ReplaceValue(
    Table.FromRecords({
        [Name = "Cindy", Country = "US", test = "zozo"],
        [Name = "Bob", Country = "CA", test = "zaza"]
    }),
  each [test] = "zaza",
   null,
    (row, test, z) =>
         if test then "?" else row ,
    {"Name", "Country"}
)

And my cmonclusions are :

• Talk about OldValue  is for me not relevant because in my example OldValueits a condition on a 3rd column . Same for or NewValue because , I can assign the condition also to a or NewValue
• Nowhere it's explained that if a custom function REPLACER is declared, why 3 paramters are mandatory and what is assigned to them ?
• The fecth on each row is not clearly explained

Thanks Rirsnfld for

• confirming that it's no so clear and that it is necessary to decipher the examples that only very partially replace an explanation of the principles
• The link Power Query M formula language to delve deeply into the architecture and specifications to better understand that.