How to Create a Column Based on If-Else-Else Conditions in Pandas?

Creating a Column with If-Else-Else Conditions in Pandas

To create a new column based on an if-elif-else condition, there are two main approaches:

Non-Vectorized Approach

This approach involves defining a function that operates on rows:

<code class="python">def f(row):
    if row['A'] == row['B']:
        val = 0
    elif row['A'] > row['B']:
        val = 1
    else:
        val = -1
    return val</code>

Then, apply it to the dataframe along the rows:

<code class="python">df['C'] = df.apply(f, axis=1)</code>

Vectorized Approach

The vectorized approach utilizes np.where to create the new column directly:

<code class="python">df['C'] = np.where(
    df['A'] == df['B'], 0, np.where(
    df['A'] >  df['B'], 1, -1)) </code>

This approach is more efficient for large datasets.

Here's an example using the provided dataframe:

Input DataFrame

A	B
2	2
3	1
1	3

Output DataFrame

A	B	C
2	2	0
3	1	1
1	3	-1

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