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pythonintermediate

Pandas Merge with Validation

Use merge() validate parameter to catch unexpected many-to-many or missing key issues in joins.

python
import pandas as pd

orders = pd.DataFrame({'order_id':[1,2,3],'product_id':[10,20,10]})
products = pd.DataFrame({'product_id':[10,20,30],'name':['Widget','Gadget','Donut']})

try:
    result = orders.merge(
        products,
        on='product_id',
        how='left',
        validate='m:1',  # each order maps to at most 1 product
    )
    print(result)
except pd.errors.MergeError as e:
    print('Merge validation failed:', e)

Use Cases

  • data integrity
  • safe joins
  • ETL validation

Tags

#pandas#merge#validation#data-quality

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