Expression.Error: We cannot convert a value of type Function to type Text - formula

Question

This M (Power Query) function gives this error "Expression.Error: We cannot convert a value of type Function to type Text."
The Function Objective is having two Text Input and subtracting them to durations (as list or text)
For Example:
1/20/2020 1:49:46 PM, 1/20/2020 1:58:03 PM, 1/20/2020 2:09:42 PM
1/20/2020 1:49:41 PM, 1/20/2020 1:57:58 PM, 1/20/2020 2:09:38 PM
let
Source = (txtCheckInTime as text, txtCheckOutTime as text) as text =>
let
lstCheckinTimeLst = Text.Split(txtCheckInTime, ", "),
lstCheckOutTimeLst = Text.Split(txtCheckOutTime, ", "),
txtCheckInEvent = each lstCheckinTimeLst,
txtCheckOutEvent = each lstCheckOutTimeLst,
EventDuration = DateTime.FromText(txtCheckInEvent) - DateTime.FromText(txtCheckOutEvent),
Source = Text.Combine(Duration.ToText(EventDuration), ", ")
in
Source
in
Source
Could anyway point out the error?

Answer 1

There are a couple of issues going on here.
The main issue is because the each keyword is a placeholder for an iterative function, not an iterator itself (see here for details).
The DateTime.FromText() function requires a single element, not a list or function object (see here for details).
It appears like in your sample data, the CheckInTime's are after the CheckOutTime's?
If I were to re-write your function, this is what it would look like:
let fun_GetDurations = (txt_CheckInTime as text, txt_CheckOutTime as text) as text =>
let
lst_CheckInTime = Text.Split(txt_CheckInTime, ", "),
lst_CheckOutTime = Text.Split(txt_CheckOutTime, ", "),
tbl_Times = Table.FromColumns({lst_CheckInTime, lst_CheckOutTime}, {"CheckInTime", "CheckOutTime"}),
fix_Formatting = Table.TransformColumns(tbl_Times, {{"CheckInTime", each DateTime.FromText(_, "en-US"), type nullable text}, {"CheckOutTime", each DateTime.FromText(_, "en-US"), type nullable text}}),
add_Duration = Table.AddColumn(fix_Formatting, "Duration", each Duration.ToText([CheckOutTime] - [CheckInTime]), type text),
get_Durations = Text.Combine(Table.Column(add_Duration, "Duration"), ", ")
in
get_Durations
in fun_GetDurations
And then when you check it:
let
txt_CheckInTime = "1/20/2020 1:49:41 PM, 1/20/2020 1:57:58 PM, 1/20/2020 2:09:38 PM",
txt_CheckOutTime = "1/20/2020 1:49:46 PM, 1/20/2020 1:58:03 PM, 1/20/2020 2:09:42 PM",
Durations = fun_GetDurations(txt_CheckInTime, txt_CheckOutTime)
in
Durations
You get the results expected:
00:00:05, 00:00:05, 00:00:04