Advanced Applications of C++ Lambda Expressions in Excel Conditional Processing

Today, we will explore a cool and practical technology—using C++ Lambda expressions to handle various conditional judgments in Excel. Lambda acts like a small function wizard that can be created anytime and anywhere, making your Excel data processing code super flexible and powerful!

1. Review of Lambda Expression Basics

Lambda expressions are anonymous function objects introduced in C++11, with the basic syntax as follows:

[capture list](parameter list) -> return type { function body }

1.1 Simplest Lambda Example

// Define a Lambda to check if a number is greater than 10
auto isGreaterThan10 = [](int num) { return num > 10; };

// Usage example
bool result = isGreaterThan10(15); // returns true

Tip: The <span>auto</span> keyword allows the compiler to automatically deduce the type of the Lambda, making it more convenient to write.

2. Implementing Excel Conditional Formatting with Lambda

2.1 Cell Condition Judgments

#include <vector>
#include <string>

struct ExcelCell {
    std::string value;
    int row;
    int col;
};

// Highlight all cells greater than a specified value
void highlightCells(std::vector<ExcelCell>& cells, 
                   int threshold) 
{
    auto condition = [threshold](const ExcelCell& cell) {
        try {
            double val = std::stod(cell.value);
            return val > threshold;
        } catch (...) {
            return false; // Non-numeric values are not processed
        }
    };

    for (auto& cell : cells) {
        if (condition(cell)) {
            std::cout << "Highlighting cell(" << cell.row << ","
                      << cell.col << "): " << cell.value << std::endl;
        }
    }
}

2.2 Multi-Condition Combination

// Check if "Technical Department and Salary > 10000"
auto isTechHighSalary = [](const Employee& emp) {
    return emp.department == "Technical Department" && emp.salary > 10000;
};

// Usage example
std::vector<Employee> techStars;
std::copy_if(employees.begin(), employees.end(),
             std::back_inserter(techStars),
             isTechHighSalary);

3. Advanced Conditional Processing Techniques

3.1 Dynamically Generating Condition Functions

// Create a Lambda generator for range checking
auto makeRangeChecker = [](double min, double max) {
    return [min, max](double value) {
        return value >= min && value <= max;
    };
};

// Usage example
auto isGradeA = makeRangeChecker(90, 100);
auto isGradeB = makeRangeChecker(80, 89);

3.2 State-Aware Condition Judgments

// Count the number of consecutive cells that meet the condition
void countConsecutive(const std::vector<ExcelCell>& cells) {
    int count = 0;
    auto resetCounter = [&count]() { count = 0; };
    
auto checkCell = [&count](const ExcelCell& cell) {
        if (cell.value == "Yes") {
            ++count;
            return true;
        }
        return false;
    };
    
    for (const auto& cell : cells) {
        if (!checkCell(cell)) {
            if (count >= 3) {
                std::cout << "Found " << count << " consecutive 'Yes' cells\n";
            }
            resetCounter();
        }
    }
}

Notes: Be cautious of lifecycle issues when capturing by reference (<span>&</span>); do not return local Lambdas.

4. Applications of Lambda in Excel Functions

4.1 Custom Sorting Rules

// Sort by string length
std::sort(cells.begin(), cells.end(),
    [](const ExcelCell& a, const ExcelCell& b) {
        return a.value.length() < b.value.length();
    });

4.2 Conditional Summary Calculations

// Calculate the average salary of the Technical Department
double avgTechSalary = std::accumulate(
    employees.begin(), employees.end(), 0.0,
    [](double sum, const Employee& emp) {
        return emp.department == "Technical Department" ? sum + emp.salary : sum;
    }) / techCount;

5. Practical Exercises

Try to implement the following functionalities:

1. Write a Lambda generator to create a condition function that “contains specific keywords”
2. Implement a multi-condition combiner that can connect multiple Lambda conditions with AND/OR
3. (Challenge) Design a condition calculation engine that supports generating Lambda conditions from string parsing

Tip: The multi-condition combiner can return a new Lambda that internally combines multiple condition checks.

6. Summary and Extensions

Today we learned:

• The basic syntax and usage scenarios of Lambda expressions
• How to implement Excel conditional formatting with Lambda
• Techniques for dynamically generating condition functions
• Applications in sorting and aggregation calculations

Advanced Directions:

1. Persistently store Lambda conditions
2. Combine with regular expressions for more powerful conditions
3. Safely use Lambda in a multithreaded environment

Remember: While Lambdas are great, avoid excessive nesting as it can affect code readability. Proper use can make your data processing code both concise and powerful!

In the next issue, we will explore how to implement Excel’s pivot table functionality using C++. If you have any questions about Lambdas, feel free to leave a comment for discussion. Don’t forget to try today’s code examples! 🚀