clg4 clg4 - 2 months ago 23
Python Question

Create Formula Based on Dynamically Changing Columns to Set Values in Pandas Dataframe Column

I am looking to create a column in a pandas dataframe that is the function of a variable/dynamic list of column names.

Typical column creation would be:

df['new']=(df['one']*x)+(df['two']*y)+(df['3']*z)


where x,y,z are variables from another df.

x 1.1
y 1.2
z 1.3
a 1.4
b 1.5
c 1.6


I want to create a column which would be a function of a variable list of columns.

So for instance if:

cols=['one','two']


then the formula would be created as:

df['new']=(df['one']*x)+(df['two']*y)


But if cols changes to:

cols=['one','two','three','four']


then the formula would change to:

df['new']=(df['one']*x)+(df['two']*y)+(df['3']*z)+(df['four']*a)


I know I must be missing something easy here.

Answer

Using zip will return the truncated pairs, so [(a, b) for a, b in zip([1, 2], [3, 4, 5, 6])] will return return [(1, 3), (2, 4)].

df = pd.DataFrame(np.random.randn(5, 5), columns=list('ABCDE'))

x = 1.1
y = 1.2
z = 1.3
a = 1.4
b = 1.5
c = 1.6

var = [x, y, z, a, b, c]
cols = ['A', 'B', 'C']

>>> sum(df[col] * v for col, v in zip(cols, var))
0    0.729284
1    2.671124
2    1.804285
3    0.791489
4    1.818327
dtype: float64
Comments