python - Subtract two columns in dataframe

Question

My df looks as follows:

Index    Country    Val1  Val2 ... Val10
1        Australia  1     3    ... 5
2        Bambua     12    33   ... 56
3        Tambua     14    34   ... 58

I'd like to substract Val10 from Val1 for each country, so output looks like:

Country    Val10-Val1
Australia  4
Bambua     23
Tambua     24

So far I've got:

def myDelta(row):
    data = row[['Val10', 'Val1']]
    return pd.Series({'Delta': np.subtract(data)})

def runDeltas():
    myDF = getDF() 
        .apply(myDelta, axis=1) 
        .sort_values(by=['Delta'], ascending=False)
    return myDF

runDeltas results in this error:

ValueError: ('invalid number of arguments', u'occurred at index 9')

What's the proper way to fix this?

Answer 1

Given the following dataframe:

df = pd.DataFrame([["Australia", 1, 3, 5],
                   ["Bambua", 12, 33, 56],
                   ["Tambua", 14, 34, 58]
                  ], columns=["Country", "Val1", "Val2", "Val10"]
                 )

It comes down to a simple broadcasting operation:

>>> df["Val1"] - df["Val10"]
0    -4
1   -44
2   -44
dtype: int64