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 

Answer 2

Using this as the df:

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

You can also do the subtraction and put it into a new column as follows.

>>>df['Val_Diff'] = df['Val10'] - df['Val1']      Country     Val1    Val2  Val10 Val_Diff 0   Australia   1       3      5    4 1   Bambua      12      33     56   44 2   Tambua      14      34     58   44