Find duplicates in a column and give a value

You can use this in a Calculated Column Anonymous 

Duplicates = 
VAR varCurrentValue = 'Sample'[Column1]
VAR varInstances = 
    COUNTROWS(
        FILTER(
            'Sample',
            'Sample'[Column1] = varCurrentValue
        )
    )
var Result = 
    IF(
        varInstances > 1,
        "Duplicate",
        "Unique"
    )
RETURN
    Result

You don't need ALL or CALCULATE. ALL in this context removes filters. Tables and Calculated Columns have no filter context, only row context.

You can try this:

Duplicates =
VAR varCurrentValue = 'Sample'[Column1]
VAR varInstances =
    COUNTROWS(
        FILTER(
            'Sample',
            'Sample'[Column1] = varCurrentValue
                && NOT 'Sample'[Column1]
                IN {
                "House",
                "Table"
            }
        )
    )
VAR Result =
    IF(
        varInstances > 1,
        "Duplicate",
        "Unique"
    )
RETURN
    Result