How to refer to a column value of a Table in measure - powerbi

Question

I have a Table in PowerBI, and it has a column which I added by New Column in PowerBI and I have a DAX function to compute the value for each row.
Then I create a new Measure for the same table. I need to create a Measure instead of Column because I need to use SelectedValue.
But for the new measure , I get error saying The value for 'MyColumn' cannot be determined. Either the column does not exist or there is no current row for this column.
Can you please tell me how can I solve this issue>?
I have a slider using the Type of Table 1, so that it has 3 selections "A", "B", "C"
Table 1
Type
A
B
C
And I have another Table 2 in m PowerBI
Table 2
Name
A Count
B Count
C Count
Paul
1
1
Jane
1
2
John
3
I want to build a measure/relationship such that if 'A' of Slider is selected, any row of Table 2 with "A count" has values will be displayed, otherwise, get it hidden.
So in this case,
when 'A' is selected, 'Paul' gets displayed,
when 'B' is selected, 'Jane', 'John' gets displayed,
when 'C' is selected, 'Paul', 'Jane' gets displayed.

Answer 1

Answer to the new question added afterwards:
For DAX calculations you want to avoid “Excel-style” crosstabs like your Table 2 at all costs. The by far easiest way to unpivot this table, would be by using PowerQuery. But if for some reason this is not possible, you can also do it "manually" in DAX:
Stacked 2 =
FILTER(
UNION(
SELECTCOLUMNS(
'Table 2',
"Name", 'Table 2'[Name],
"Attribute", "A Count",
"Value", 'Table 2'[A Count]),
SELECTCOLUMNS(
'Table 2',
"Name", 'Table 2'[Name],
"Attribute", "B Count",
"Value", 'Table 2'[B Count]),
SELECTCOLUMNS(
'Table 2',
"Name", 'Table 2'[Name],
"Attribute", "C Count",
"Value", 'Table 2'[C Count])
),
NOT ISBLANK([Value])
)
The result of this Calculated Table will look like this:
Now you need to extend your "Table 1" by a corresponding Calculated Column:
Attribute = 'Table 1'[Type] & " Count"
All that is left is to create a relationship between the 2 Attribute columns and you're done:
Put 'Table 1'[Type] in a slicer and 'Stacked 2'[Name'] in a table visual and everything will work like a charm:

Answer 2

What you experience is the row context. This only exists in a calculated column, not in a measure. The idea of a measure is to aggregate values in "vertical direction", in a column, whereas a calculated column does calculations in "horizontal direction", row by row.
Bottom line: In measures you always have to use aggregator functions, like SUM(), COUNT(), MIN() around a column reference, e.g.
Measure = SUM('Table'[Column])
But if you still need a row context in a measure, you can use an iterator function like SUMX(), which iterates over a table row by row, thereby establishing the row context, e.g.
Measure =
SUMX(
'Table',
'Table'[Column A] * 'Table'[Column B]
)
which will create a sum product of 'Table'[Column A] and 'Table'[Column B].
Note that if your table happens to have an unique ID column, you can filter your aggregating measure by this column and you'll get values for every row, effectively "removing" the aggregation.