Step 4: Categorize Transactions

Map Merchant Category Codes (MCC) to human-readable categories for analytics. This replaces DataStage Switch/Case stages with Expanso's match expression.

The Goal

Convert numeric MCC codes like 5411 into readable categories like GROCERY for:

• Dashboard filtering
• Spending analytics
• Fraud detection rules

DataStage Equivalent

In DataStage, categorization typically requires:

1. Switch/Case Stage with dozens of conditions
2. Lookup Table maintained in a separate database
3. Default handling for unknown codes

Expanso simplifies this with inline match expressions that use pattern matching.

Implementation

See the categorization processor in the canonical reference and its captured input and output in the Explorer.

Understanding the Code

Expression	What It Does
.string()	Convert MCC to string for pattern matching
match $mcc {...}	Pattern matching expression
this.has_prefix("54")	Check if string starts with "54"
||	Logical OR for multiple prefixes
_ => "OTHER"	Default case (underscore = wildcard)

MCC Code Reference

Common MCC prefixes and their meanings:

Prefix	Category	Examples
54xx	Grocery	Supermarkets, food stores
55xx	Automotive	Gas stations, auto dealers
58xx	Restaurant	Fast food, dining
59xx	Retail	Department stores, misc retail
47xx	Transportation	Airlines, rail, taxi
40-41xx	Travel	Hotels, lodging
60-61xx	Financial	Banks, insurance
80xx	Professional	Legal, medical, accounting

Expected Output

Input:

{
  "MERCHANT_CATEGORY_CODE": "5411",
  "MERCHANT_NAME": "ACME Electronics GmbH",
  ...
}

Output:

{
  "MERCHANT_CATEGORY_CODE": "5411",
  "MERCHANT_NAME": "ACME Electronics GmbH",
  "transaction_category": "GROCERY",
  ...
}

Production Considerations

Exact MCC Matching

For precise MCC codes instead of prefixes:

Partial snippet

- mapping: |
    root = this
    let mcc_map = {
      "5411": "GROCERY_SUPERMARKET",
      "5412": "GROCERY_CONVENIENCE",
      "5541": "GAS_STATION",
      "5542": "GAS_AUTOMATED"
    }

    root.transaction_category = $mcc_map.get(this.MERCHANT_CATEGORY_CODE.string()).or("OTHER")

External Category Lookup

Load categories from a file or API:

Partial snippet

# Partial snippet: load MCC mappings from a local file at startup.
input:
  file:
    paths: ['mcc-categories.json']

Subcategories

Add hierarchical categorization:

Partial snippet

- mapping: |
    root = this
    let mcc = this.MERCHANT_CATEGORY_CODE.string()
    root.category_level1 = match $mcc {
    this.has_prefix("5") => "RETAIL",
    this.has_prefix("4") => "TRAVEL",
    this.has_prefix("6") => "FINANCIAL",
    _ => "OTHER"
    }

    root.category_level2 = match $mcc {
    this.has_prefix("54") => "GROCERY",
    this.has_prefix("58") => "DINING",
    _ => root.category_level1
    }

Flagging High-Risk Categories

Add fraud indicators:

Partial snippet

- mapping: |
    root = this
    let mcc = this.MERCHANT_CATEGORY_CODE.string()
    root.high_risk = match $mcc {
      this.has_prefix("59") => true,   # Misc retail
      this.has_prefix("79") => true,   # Recreation
      this.has_prefix("76") => true,   # Misc services
      _ => false
    }

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Next Step

📖 Step 5: Standardize Schema →