List.Buffer (Will it refresh automatically?)

[Tom_Y]

Hi,

I'm having these 3 lines in power query to get the column headers of multiple tables before I go back and expand them, so all columns in all tables are extracted. It's too slow until I add "List.Buffer" to the list HEADINGS, and it's now running smoothly.

Somewhere said the buffered list is stored in memory. Will it be updated when I click refresh, or scheduled refreshing (BI Services) in mid-night? I'm afraid new columns are added in one of those tables, and the code do not update and extract the data. Thanks in advance.

PreExpand = Table.SelectColumns(#"Invoke Custom Function1",{"Transform File"}),

HEADINGS = List.Buffer(List.Union(List.Transform(PreExpand[Transform File], each Table.ColumnNames(_)))),
ReadyToExpand = PreExpand,
#"Expanded Transform File" = Table.ExpandTableColumn(ReadyToExpand, "Transform File", HEADINGS)

[lbendlin · Accepted solution]

List.Buffer has no logic or meta data impact on your transforms, it "only"  improves their performance.

You may also want to List.Buffer the column names.