def _dropSparseCol(df,thresh):
    """
    Return DataFrame with subset of columns that a proportion of nonNaN entries to total entries above `thresh`
    
    @param thresh: float defining the threshold for the proportion of filled values in a column. 
    Keep all columns above this values
    
    @param df: pandas DataFrame
    """
    isNotSparse = (df.describe().loc[ 'count' ,:].values)/len(df.index) >= thresh
    df_dropCol = df.iloc[:,isNotSparse]
    return df_dropCol