Interpolate missing data with group by column

ronrsnfld straight line interpolation between the points surrounding the missing values is what I'm looking for.

Out of town now. But have a method for straight line Interpolation of missing data points ignoring missing data at very start or end. Will post later this week.

Unable to download your file.

Below is code that

• interpolates missing values using a "straight-line" between the entries surrounding the missing values
• If the sequence starts with a null or series of nulls, those will be ignored.
• If the sequence ends with a null or series of nulls, those will be ignored.

Custom function to do the interpolateion

Rename a blank query => fnStraightLineInterpolation

(t as table)=>

let 
    #"Grouped Rows" = Table.Group(t, {"value"}, {
        {"Null Count", each if [value]{0}=null then List.Count([value]) else 0, Int64.Type}},
        GroupKind.Local),
    
    #"Shifted" = Table.FromColumns(
            Table.ToColumns(#"Grouped Rows")
            & {List.RemoveFirstN(#"Grouped Rows"[value] & {null})}
            & {{null} & List.RemoveLastN(#"Grouped Rows"[value])},
            type table[value=number,Null Count=Int64.Type, after Null=number, before Null=number]),

    #"Added Custom" = Table.AddColumn(Shifted, "Interpolation", each 
        if [Null Count] = 0 then {[value]}
            else let 
                    increment = ([after Null] - [before Null]) / ([Null Count]+1),
                    values = if increment = null
                                then List.Repeat({null},[Null Count])
                                else List.Numbers([before Null] + increment, [Null Count], increment)
                in 
                    values, type list),

//Merge back with Datetime and Name columns
    #"Result" = Table.FromColumns(
                    Table.ToColumns(Table.SelectColumns(t,{"Datetime","Name"}))
                    & {List.Combine(#"Added Custom"[Interpolation])},
                type table[Datetime=datetime, Name=text, Value=number])

in
    #"Result"

Main Query

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("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", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Datetime = _t, Name = _t, value = _t]),
    #"Added Suffix" = Table.TransformColumns(Source, {{"Datetime", each _ & ":00", type text}}),
    #"Changed Type with Locale" = Table.TransformColumnTypes(#"Added Suffix", {{"Datetime", type datetime}}, "en-NA"),
    #"Changed Type" = Table.TransformColumnTypes(#"Changed Type with Locale",{{"value", type number}}),
   
//Group by Name
//  then interpolate each subgroup
    #"Grouped Rows" = Table.Group(#"Changed Type", {"Name"}, {
        {"All", each fnStraightLineInterpolation(_)}}),

//Remove unneeded column and Expand the table
    #"Removed Columns" = Table.RemoveColumns(#"Grouped Rows",{"Name"}),
    #"Expanded All" = Table.ExpandTableColumn(#"Removed Columns", "All", {"Datetime", "Name", "Value"}, {"Datetime", "Name", "Value"}),
    #"Changed Type1" = Table.TransformColumnTypes(#"Expanded All",{{"Datetime", type datetime}, {"Name", type text}, {"Value", type number}})
        
in
    #"Changed Type1"

Part of output after interpolation

Graphic output before and after processing