def extract_array_column(a, col):
    """Extracts a column from a tabular structure
 
    @type a:  list/tuple
    @param a: an array of equal-sized arrays, representing
              a table as a list of rows.
    @type col:  usually int or str
    @param col: the column key of the column to extract

    @rtype:  list
    @return: the values of column col from each row in a

    """
    column = []
    
    for r in a:
        column.append( r[col] )
    
    return column