forEach Function - DataFrame Library Documentation

Overview

The forEach function iterates over each element in a Serie to perform an operation without changing the Serie itself. It's useful for side effects like printing or accumulating values.

Function Signatures


          // Single serie version
          template <typename F, typename T>
          auto forEach(F&& callback, const Serie<T>& serie);
          
          // Multi-series version
          template <typename F, typename T, typename... Args>
          auto forEach(F&& callback, const Serie<T>& first, const Serie<T>& second, const Args&... args);
          
          // Member function version
          template <typename F>
          void Serie<T>::forEach(F&& callback) const;
          
          // Bound version for pipeline operations
          template <typename F> auto bind_forEach(F&& callback);

Parameters

Parameter	Type	Description
callback	F&& (callable)	Function to apply to each element. For single Serie version, should accept `(T value, size_t index)`. For multi-Serie version, should accept `(T first_value, U second_value, ... args_values, size_t index)`.
serie	const Serie<T>&	The Serie to iterate over.
first, second, args...	const Serie<T>&, const Serie<U>&, ...	Multiple Series to iterate over in parallel.

Return Value

The forEach function does not return a value (void). It is used for its side effects.

Example Usage

Single Serie Example


// Create a Serie
df::Serie<int> numbers{1, 2, 3, 4, 5};

// Using Serie member function
numbers.forEach([](int value, size_t index) {
    std::cout << "Element " << index << ": " << value << std::endl;
});

// Using free function
df::forEach([](int value, size_t index) {
    std::cout << "Element " << index << ": " << value << std::endl;
}, numbers);

// Calculate sum (using a side effect)
int sum = 0;
numbers.forEach([&sum](int value, size_t) {
    sum += value;
});
std::cout << "Sum: " << sum << std::endl;  // Output: Sum: 15

Multiple Series Example


// Create multiple Series
df::Serie<std::string> names{"Alice", "Bob", "Charlie"};
df::Serie<int> ages{25, 32, 28};
df::Serie<double> heights{165.5, 180.2, 175.0};

// Process multiple Series together
df::forEach([](const std::string& name, int age, double height, size_t index) {
    std::cout << "Person " << index << ": " 
              << name << ", age " << age 
              << ", height " << height << " cm" << std::endl;
}, names, ages, heights);

// Output:
// Person 0: Alice, age 25, height 165.5 cm
// Person 1: Bob, age 32, height 180.2 cm
// Person 2: Charlie, age 28, height 175 cm

Pipeline Example


// Create a Serie
df::Serie<double> values{1.1, 2.2, 3.3, 4.4, 5.5};

// Use bind_forEach in a pipeline
values | df::bind_forEach([](double value, size_t index) {
    std::cout << "Value at " << index << ": " << value << std::endl;
});

// Multiple operations in a pipeline
df::Serie<int> numbers{1, 2, 3, 4, 5};
int sum = 0;

numbers
    | df::bind_map([](int x, size_t) { return x * 2; })  // Double each value
    | df::bind_forEach([&sum](int value, size_t) {       // Sum the doubled values
        sum += value;
    });
    
std::cout << "Sum of doubled values: " << sum << std::endl;  // Output: 30

Implementation Notes

The forEach function does not modify the input Serie(s).
For multiple Series, all Series must have the same size.
The callback function is called once for each element, in order from first to last.
The index parameter is optional in the callback function.

forEach