How to compare two values in different rows AND different columns in pandas-CodePudding

I have it currently working comparing two values on the same row but different columns but I need it to compare one value to the previous row.

For example: I need to compare the column 'Close' of the row at index 0 to the column 'Open' of the row at index 1.

df['HigherLower'] = 'No Change'

for index, row in df.iterrows():
    if row['Open'] < row['Close'] :
        df['HigherLower'] = df['HigherLower'].replace(['No Change'],'Lower')
    else:
        df['HigherLower'] = df['HigherLower'].replace(['No Change'],'Higher')

CodePudding user response：

Use np.where:

import pandas as pd
import numpy as np

df = pd.DataFrame({'Open': [10, 20, 30], 'Close': [5, 25, 15]})

df['HigherLower'] = np.where(df['Open'].shift() < df['Close'], 'Lower', 'Higher')
print(df)

# Output:
   Open  Close HigherLower
0    10      5      Higher
1    20     25       Lower
2    30     15      Higher