CWICR Assembly Builder

Business Case

Problem Statement

Estimating repetitive elements requires:

• Consistent item groupings
• Reusable templates
• Standard assemblies
• Quick application

Solution

Build and manage assemblies of CWICR work items that can be applied as templates to speed up estimating and ensure completeness.

Business Value

• Speed - Apply complete assemblies quickly
• Consistency - Standard item groupings
• Completeness - No missed items
• Reusability - Template library

Technical Implementation

python
import pandas as pd
import json
from typing import Dict, Any, List, Optional
from dataclasses import dataclass, field
from enum import Enum
from datetime import datetime


class AssemblyType(Enum):
    """Types of assemblies."""
    STRUCTURAL = "structural"
    ARCHITECTURAL = "architectural"
    MECHANICAL = "mechanical"
    ELECTRICAL = "electrical"
    SITEWORK = "sitework"
    GENERAL = "general"


@dataclass
class AssemblyItem:
    """Single item in assembly."""
    work_item_code: str
    description: str
    quantity_per_unit: float  # Quantity per assembly unit
    unit: str
    unit_cost: float
    total_cost: float
    notes: str = ""


@dataclass
class Assembly:
    """Complete assembly definition."""
    assembly_code: str
    name: str
    description: str
    assembly_type: AssemblyType
    unit: str  # Assembly unit (e.g., "m2", "each", "LF")
    items: List[AssemblyItem]
    total_cost_per_unit: float
    labor_hours_per_unit: float
    created_date: datetime
    version: int = 1


class CWICRAssemblyBuilder:
    """Build and manage assemblies from CWICR data."""

    def __init__(self, cwicr_data: pd.DataFrame):
        self.cwicr = cwicr_data
        self._index_cwicr()
        self._assemblies: Dict[str, Assembly] = {}

    def _index_cwicr(self):
        """Index CWICR data."""
        if 'work_item_code' in self.cwicr.columns:
            self._cwicr_index = self.cwicr.set_index('work_item_code')
        else:
            self._cwicr_index = None

    def _get_item_cost(self, code: str) -> Tuple[float, float, str]:
        """Get item unit cost and labor hours."""
        if self._cwicr_index is None or code not in self._cwicr_index.index:
            return (0, 0, 'unit')

        item = self._cwicr_index.loc[code]
        labor = float(item.get('labor_cost', 0) or 0)
        material = float(item.get('material_cost', 0) or 0)
        equipment = float(item.get('equipment_cost', 0) or 0)
        labor_hours = float(item.get('labor_norm', item.get('labor_hours', 0)) or 0)
        unit = str(item.get('unit', 'unit'))

        return (labor + material + equipment, labor_hours, unit)

    def create_assembly(self,
                        assembly_code: str,
                        name: str,
                        description: str,
                        assembly_type: AssemblyType,
                        unit: str,
                        items: List[Dict[str, Any]]) -> Assembly:
        """Create new assembly from work items."""

        assembly_items = []
        total_cost = 0
        total_hours = 0

        for item_def in items:
            code = item_def.get('work_item_code', item_def.get('code'))
            qty_per_unit = item_def.get('quantity_per_unit', 1)
            notes = item_def.get('notes', '')

            unit_cost, labor_hours, item_unit = self._get_item_cost(code)

            # Get description from CWICR
            if self._cwicr_index is not None and code in self._cwicr_index.index:
                desc = str(self._cwicr_index.loc[code].get('description', code))
            else:
                desc = item_def.get('description', code)

            item_total = unit_cost * qty_per_unit

            assembly_items.append(AssemblyItem(
                work_item_code=code,
                description=desc,
                quantity_per_unit=qty_per_unit,
                unit=item_unit,
                unit_cost=round(unit_cost, 2),
                total_cost=round(item_total, 2),
                notes=notes
            ))

            total_cost += item_total
            total_hours += labor_hours * qty_per_unit

        assembly = Assembly(
            assembly_code=assembly_code,
            name=name,
            description=description,
            assembly_type=assembly_type,
            unit=unit,
            items=assembly_items,
            total_cost_per_unit=round(total_cost, 2),
            labor_hours_per_unit=round(total_hours, 2),
            created_date=datetime.now(),
            version=1
        )

        self._assemblies[assembly_code] = assembly
        return assembly

    def apply_assembly(self,
                        assembly_code: str,
                        quantity: float,
                        location_factor: float = 1.0) -> Dict[str, Any]:
        """Apply assembly to get estimate."""

        assembly = self._assemblies.get(assembly_code)
        if assembly is None:
            return {'error': f"Assembly {assembly_code} not found"}

        items = []
        total_cost = 0
        total_hours = 0

        for item in assembly.items:
            qty = item.quantity_per_unit * quantity
            cost = item.total_cost * quantity * location_factor
            hours = qty * (item.unit_cost / 50 if item.unit_cost > 0 else 0)  # Approximate labor hours

            items.append({
                'work_item_code': item.work_item_code,
                'description': item.description,
                'quantity': round(qty, 2),
                'unit': item.unit,
                'cost': round(cost, 2)
            })

            total_cost += cost
            total_hours += hours

        return {
            'assembly_code': assembly_code,
            'assembly_name': assembly.name,
            'quantity': quantity,
            'unit': assembly.unit,
            'location_factor': location_factor,
            'items': items,
            'total_cost': round(total_cost, 2),
            'total_labor_hours': round(total_hours, 2),
            'cost_per_unit': round(total_cost / quantity, 2) if quantity > 0 else 0
        }

    def get_assembly(self, assembly_code: str) -> Optional[Assembly]:
        """Get assembly by code."""
        return self._assemblies.get(assembly_code)

    def list_assemblies(self, assembly_type: AssemblyType = None) -> List[Dict[str, Any]]:
        """List all assemblies."""

        assemblies = self._assemblies.values()

        if assembly_type:
            assemblies = [a for a in assemblies if a.assembly_type == assembly_type]

        return [
            {
                'code': a.assembly_code,
                'name': a.name,
                'type': a.assembly_type.value,
                'unit': a.unit,
                'cost_per_unit': a.total_cost_per_unit,
                'item_count': len(a.items)
            }
            for a in assemblies
        ]

    def clone_assembly(self,
                        source_code: str,
                        new_code: str,
                        new_name: str = None) -> Optional[Assembly]:
        """Clone existing assembly."""

        source = self._assemblies.get(source_code)
        if source is None:
            return None

        new_assembly = Assembly(
            assembly_code=new_code,
            name=new_name or f"{source.name} (Copy)",
            description=source.description,
            assembly_type=source.assembly_type,
            unit=source.unit,
            items=source.items.copy(),
            total_cost_per_unit=source.total_cost_per_unit,
            labor_hours_per_unit=source.labor_hours_per_unit,
            created_date=datetime.now(),
            version=1
        )

        self._assemblies[new_code] = new_assembly
        return new_assembly

    def compare_assemblies(self,
                            codes: List[str],
                            quantity: float = 1) -> pd.DataFrame:
        """Compare multiple assemblies."""

        data = []

        for code in codes:
            assembly = self._assemblies.get(code)
            if assembly:
                result = self.apply_assembly(code, quantity)
                data.append({
                    'Assembly': assembly.name,
                    'Code': code,
                    'Unit': assembly.unit,
                    'Cost/Unit': assembly.total_cost_per_unit,
                    'Hours/Unit': assembly.labor_hours_per_unit,
                    f'Total ({quantity} {assembly.unit})': result['total_cost'],
                    'Items': len(assembly.items)
                })

        return pd.DataFrame(data)

    def create_standard_assemblies(self):
        """Create standard construction assemblies."""

        # Concrete slab assembly
        self.create_assembly(
            assembly_code="SLAB-100",
            name="Concrete Slab 100mm",
            description="Standard 100mm concrete slab on grade",
            assembly_type=AssemblyType.STRUCTURAL,
            unit="m2",
            items=[
                {'code': 'PREP-001', 'quantity_per_unit': 1.0, 'notes': 'Subgrade preparation'},
                {'code': 'GRAVEL-001', 'quantity_per_unit': 0.15, 'notes': '150mm gravel base'},
                {'code': 'VAPOR-001', 'quantity_per_unit': 1.1, 'notes': 'Vapor barrier'},
                {'code': 'MESH-001', 'quantity_per_unit': 1.1, 'notes': 'Welded wire mesh'},
                {'code': 'CONC-001', 'quantity_per_unit': 0.1, 'notes': '100mm concrete'},
                {'code': 'FINISH-001', 'quantity_per_unit': 1.0, 'notes': 'Power trowel finish'}
            ]
        )

        # Stud wall assembly
        self.create_assembly(
            assembly_code="WALL-STUD",
            name="Metal Stud Wall",
            description="Metal stud wall with drywall both sides",
            assembly_type=AssemblyType.ARCHITECTURAL,
            unit="m2",
            items=[
                {'code': 'TRACK-001', 'quantity_per_unit': 0.8, 'notes': 'Floor/ceiling track'},
                {'code': 'STUD-001', 'quantity_per_unit': 2.5, 'notes': 'Studs @ 400mm OC'},
                {'code': 'INSUL-001', 'quantity_per_unit': 1.0, 'notes': 'Batt insulation'},
                {'code': 'GYP-001', 'quantity_per_unit': 2.2, 'notes': 'Drywall both sides'},
                {'code': 'TAPE-001', 'quantity_per_unit': 2.0, 'notes': 'Tape and mud'}
            ]
        )

    def export_assemblies(self, output_path: str) -> str:
        """Export assemblies to Excel."""

        with pd.ExcelWriter(output_path, engine='openpyxl') as writer:
            # Summary
            summary_df = pd.DataFrame([
                {
                    'Code': a.assembly_code,
                    'Name': a.name,
                    'Type': a.assembly_type.value,
                    'Unit': a.unit,
                    'Cost/Unit': a.total_cost_per_unit,
                    'Hours/Unit': a.labor_hours_per_unit,
                    'Items': len(a.items),
                    'Version': a.version
                }
                for a in self._assemblies.values()
            ])
            summary_df.to_excel(writer, sheet_name='Assemblies', index=False)

            # Details for each assembly
            for code, assembly in self._assemblies.items():
                if len(code) > 25:
                    sheet_name = code[:25]
                else:
                    sheet_name = code

                detail_df = pd.DataFrame([
                    {
                        'Work Item': item.work_item_code,
                        'Description': item.description,
                        'Qty/Unit': item.quantity_per_unit,
                        'Item Unit': item.unit,
                        'Unit Cost': item.unit_cost,
                        'Total Cost': item.total_cost,
                        'Notes': item.notes
                    }
                    for item in assembly.items
                ])
                detail_df.to_excel(writer, sheet_name=sheet_name, index=False)

        return output_path

    def save_library(self, filepath: str):
        """Save assembly library to JSON."""
        data = {}

        for code, assembly in self._assemblies.items():
            data[code] = {
                'assembly_code': assembly.assembly_code,
                'name': assembly.name,
                'description': assembly.description,
                'assembly_type': assembly.assembly_type.value,
                'unit': assembly.unit,
                'items': [
                    {
                        'work_item_code': item.work_item_code,
                        'description': item.description,
                        'quantity_per_unit': item.quantity_per_unit,
                        'unit': item.unit,
                        'notes': item.notes
                    }
                    for item in assembly.items
                ],
                'version': assembly.version
            }

        with open(filepath, 'w') as f:
            json.dump(data, f, indent=2)

Quick Start

python
# Load CWICR data
cwicr = pd.read_parquet("TR_workitems_costs_resources_DDC_CWICR.parquet")

# Initialize builder
builder = CWICRAssemblyBuilder(cwicr)

# Create assembly
builder.create_assembly(
    assembly_code="FDN-STRIP",
    name="Strip Foundation",
    description="Standard strip foundation 600x300",
    assembly_type=AssemblyType.STRUCTURAL,
    unit="LM",
    items=[
        {'code': 'EXCV-001', 'quantity_per_unit': 0.5},
        {'code': 'CONC-001', 'quantity_per_unit': 0.18},
        {'code': 'REBAR-001', 'quantity_per_unit': 15}
    ]
)

# Apply assembly
result = builder.apply_assembly("FDN-STRIP", quantity=50)
print(f"Total Cost: ${result['total_cost']:,.2f}")

Common Use Cases

1. Standard Assemblies

python
builder.create_standard_assemblies()
assemblies = builder.list_assemblies()
for a in assemblies:
    print(f"{a['code']}: ${a['cost_per_unit']:.2f}/{a['unit']}")

2. Compare Options

python
comparison = builder.compare_assemblies(
    ["WALL-STUD", "WALL-BLOCK"],
    quantity=100
)
print(comparison)

3. Clone and Modify

python
builder.clone_assembly("SLAB-100", "SLAB-150", "Concrete Slab 150mm")

Resources

• GitHub: OpenConstructionEstimate-DDC-CWICR
• DDC Book: Chapter 3.1 - Assembly-Based Estimating