Standard Error

/**
 * Fintech Math Bootcamp · Lesson 076 of 120
 * Standard Error
 * Module 08: Sampling, Estimation, and Statistical Inference
 *
 * Scenario: Measuring uncertainty in a mean rather than variation among payments
 * Rule:     estimated SE(mean) = sample SD / √n
 *
 * Try it:   Which is the larger number here: sample SD or mean SE?
 *
 * Lesson article: https://thefintechbuilder.com/financial-mathematics-statistics-and-data-foundations/sampling-estimation-and-statistical-inference/standard-error/
 * Free course:    https://courses.thefintechbuilder.com
 * Synthetic teaching example, not financial advice or a production library.
 */

export function lesson076() {
  const x=[2,3,3,4,4];
  const mean=x.reduce((s,v)=>s+v,0)/x.length;
  const variance=x.reduce((s,v)=>s+(v-mean)**2,0)/(x.length-1);
  const result={mean,sd:Math.sqrt(variance),se:Math.sqrt(variance/x.length)};
  return result;
}

export const checkedResult = {"mean":3.2,"sd":0.8366600265340756,"se":0.3741657386773941};

// Run this file directly: npx tsx lessons/08-sampling-estimation-and-statistical-inference/076-standard-error.ts
if (process.argv[1] && import.meta.url.endsWith(process.argv[1].replace(/\\/g, "/").split("/").pop()!)) {
  console.log(JSON.stringify(lesson076(), null, 2));
}

"""
Fintech Math Bootcamp · Lesson 076 of 120
Standard Error
Module 08: Sampling, Estimation, and Statistical Inference

Scenario: Measuring uncertainty in a mean rather than variation among payments
Rule:     estimated SE(mean) = sample SD / √n

Try it:   Which is the larger number here: sample SD or mean SE?

Lesson article: https://thefintechbuilder.com/financial-mathematics-statistics-and-data-foundations/sampling-estimation-and-statistical-inference/standard-error/
Free course:    https://courses.thefintechbuilder.com
Synthetic teaching example, not financial advice or a production library.
"""

import json
import math


def lesson_076():
    x = [2, 3, 3, 4, 4]
    total = 0
    for v in x:
        total += v
    mean = total / len(x)
    squares = 0
    for v in x:
        squares += (v - mean) ** 2
    variance = squares / (len(x) - 1)
    return {"mean": mean, "sd": math.sqrt(variance), "se": math.sqrt(variance / len(x))}


if __name__ == "__main__":
    print(json.dumps(lesson_076(), indent=2))

// Fintech Math Bootcamp - Lesson 076 of 120
// Standard Error
// Module 08: Sampling, Estimation, and Statistical Inference
//
// Scenario: Measuring uncertainty in a mean rather than variation among payments
// Rule:     estimated SE(mean) = sample SD / sqrt(n)
//
// Try it:   Which is the larger number here: sample SD or mean SE?
//
// Lesson article: https://thefintechbuilder.com/financial-mathematics-statistics-and-data-foundations/sampling-estimation-and-statistical-inference/standard-error/
// Free course:    https://courses.thefintechbuilder.com
// Synthetic teaching example, not financial advice or a production library.
import java.util.ArrayList;
import java.util.Arrays;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

public class Main {
    static Map<String, Object> lesson076() {
        double[] x = {2, 3, 3, 4, 4};
        double total = 0;
        for (double v : x) total += v;
        double mean = total / x.length;
        double squares = 0;
        for (double v : x) squares += Math.pow(v - mean, 2);
        double variance = squares / (x.length - 1);
        Map<String, Object> result = new LinkedHashMap<String, Object>();
        result.put("mean", mean);
        result.put("sd", Math.sqrt(variance));
        result.put("se", Math.sqrt(variance / x.length));
        return result;
    }

    public static void main(String[] args) {
        System.out.println(toJson(lesson076(), ""));
    }

    // Minimal JSON writer: two-space indent, whole numbers without a decimal point, NaN as null.
    static String toJson(Object value, String indent) {
        if (value == null) return "null";
        if (value instanceof Boolean) return value.toString();
        if (value instanceof Number) return formatNumber(((Number) value).doubleValue());
        if (value instanceof String) return quote((String) value);
        if (value instanceof double[]) {
            List<Object> boxed = new ArrayList<Object>();
            for (double d : (double[]) value) boxed.add(d);
            return toJson(boxed, indent);
        }
        if (value instanceof Object[]) return toJson(Arrays.asList((Object[]) value), indent);
        String inner = indent + "  ";
        StringBuilder out = new StringBuilder();
        if (value instanceof Map) {
            Map<?, ?> map = (Map<?, ?>) value;
            if (map.isEmpty()) return "{}";
            out.append("{\n");
            int i = 0;
            for (Map.Entry<?, ?> entry : map.entrySet()) {
                out.append(inner).append(quote(entry.getKey().toString())).append(": ")
                   .append(toJson(entry.getValue(), inner));
                out.append(++i < map.size() ? ",\n" : "\n");
            }
            return out.append(indent).append("}").toString();
        }
        List<?> list = (List<?>) value;
        if (list.isEmpty()) return "[]";
        out.append("[\n");
        for (int i = 0; i < list.size(); i++) {
            out.append(inner).append(toJson(list.get(i), inner));
            out.append(i + 1 < list.size() ? ",\n" : "\n");
        }
        return out.append(indent).append("]").toString();
    }

    static String formatNumber(double x) {
        if (Double.isNaN(x) || Double.isInfinite(x)) return "null";
        if (x == Math.rint(x) && Math.abs(x) < 1e15) return Long.toString((long) x);
        return Double.toString(x);
    }

    static String quote(String s) {
        StringBuilder out = new StringBuilder("\"");
        for (char c : s.toCharArray()) {
            if (c == '"' || c == '\\') out.append('\\').append(c);
            else if (c == '\n') out.append("\\n");
            else if (c < 0x20) out.append(String.format("\\u%04x", (int) c));
            else out.append(c);
        }
        return out.append('"').toString();
    }
}

// Fintech Math Bootcamp · Lesson 076 of 120
// Standard Error
// Module 08: Sampling, Estimation, and Statistical Inference
//
// Scenario: Measuring uncertainty in a mean rather than variation among payments
// Rule:     estimated SE(mean) = sample SD / √n
//
// Try it:   Which is the larger number here: sample SD or mean SE?
//
// Lesson article: https://thefintechbuilder.com/financial-mathematics-statistics-and-data-foundations/sampling-estimation-and-statistical-inference/standard-error/
// Free course:    https://courses.thefintechbuilder.com
// Synthetic teaching example, not financial advice or a production library.
package main

import (
	"encoding/json"
	"fmt"
	"math"
)

type Lesson076Result struct {
	Mean float64 `json:"mean"`
	SD   float64 `json:"sd"`
	SE   float64 `json:"se"`
}

func lesson076() Lesson076Result {
	x := []float64{2, 3, 3, 4, 4}
	n := float64(len(x))
	total := 0.0
	for _, v := range x {
		total += v
	}
	mean := total / n
	squares := 0.0
	for _, v := range x {
		squares += math.Pow(v-mean, 2)
	}
	variance := squares / (n - 1)
	return Lesson076Result{Mean: mean, SD: math.Sqrt(variance), SE: math.Sqrt(variance / n)}
}

func main() {
	out, err := json.MarshalIndent(lesson076(), "", "  ")
	if err != nil {
		panic(err)
	}
	fmt.Println(string(out))
}

// Fintech Math Bootcamp · Lesson 076 of 120
// Standard Error
// Module 08: Sampling, Estimation, and Statistical Inference
//
// Scenario: Measuring uncertainty in a mean rather than variation among payments
// Rule:     estimated SE(mean) = sample SD / √n
//
// Try it:   Which is the larger number here: sample SD or mean SE?
//
// Lesson article: https://thefintechbuilder.com/financial-mathematics-statistics-and-data-foundations/sampling-estimation-and-statistical-inference/standard-error/
// Free course:    https://courses.thefintechbuilder.com
// Synthetic teaching example, not financial advice or a production library.
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <optional>
#include <stdexcept>
#include <string>
#include <utility>
#include <vector>

// A minimal JSON value, enough to print this lesson's result.
struct Json {
    enum class Kind { Null, Bool, Number, String, Array, Object };
    Kind kind = Kind::Null;
    bool flag = false;
    double number = 0.0;
    std::string text;
    std::vector<std::string> keys;  // object keys, parallel to items
    std::vector<Json> items;        // array elements or object values

    Json() = default;
    Json(bool value) : kind(Kind::Bool), flag(value) {}
    Json(int value) : kind(Kind::Number), number(value) {}
    Json(double value) : kind(Kind::Number), number(value) {}
    Json(const char* value) : kind(Kind::String), text(value) {}
    Json(const std::string& value) : kind(Kind::String), text(value) {}
    Json(const std::vector<double>& values) : kind(Kind::Array) {
        for (double v : values) items.push_back(Json(v));
    }
};

Json jsonArray(const std::vector<Json>& values) {
    Json array;
    array.kind = Json::Kind::Array;
    array.items = values;
    return array;
}

Json jsonObject(const std::vector<std::pair<std::string, Json>>& fields) {
    Json object;
    object.kind = Json::Kind::Object;
    for (const auto& field : fields) {
        object.keys.push_back(field.first);
        object.items.push_back(field.second);
    }
    return object;
}

// Shortest decimal form that reads back as the same double.
std::string formatNumber(double x) {
    if (!std::isfinite(x)) return "null";
    char buffer[32];
    if (x == std::floor(x) && std::fabs(x) < 1e15) {
        std::snprintf(buffer, sizeof buffer, "%.0f", x);
        return buffer;
    }
    for (int precision = 1; precision <= 17; ++precision) {
        std::snprintf(buffer, sizeof buffer, "%.*g", precision, x);
        if (std::strtod(buffer, nullptr) == x) break;
    }
    return buffer;
}

std::string quote(const std::string& s) {
    std::string out = "\"";
    for (char c : s) {
        if (c == '"' || c == '\\') { out += '\\'; out += c; }
        else if (c == '\n') out += "\\n";
        else out += c;
    }
    return out + "\"";
}

std::string toJson(const Json& value, const std::string& indent = "") {
    switch (value.kind) {
        case Json::Kind::Null: return "null";
        case Json::Kind::Bool: return value.flag ? "true" : "false";
        case Json::Kind::Number: return formatNumber(value.number);
        case Json::Kind::String: return quote(value.text);
        default: break;
    }
    const bool isObject = value.kind == Json::Kind::Object;
    if (value.items.empty()) return isObject ? "{}" : "[]";
    const std::string inner = indent + "  ";
    std::string out = isObject ? "{\n" : "[\n";
    for (std::size_t i = 0; i < value.items.size(); ++i) {
        out += inner;
        if (isObject) out += quote(value.keys[i]) + ": ";
        out += toJson(value.items[i], inner);
        out += i + 1 < value.items.size() ? ",\n" : "\n";
    }
    return out + indent + (isObject ? "}" : "]");
}

Json lesson076() {
    const std::vector<double> x = {2, 3, 3, 4, 4};
    const double n = static_cast<double>(x.size());
    double total = 0.0;
    for (double v : x) total += v;
    const double mean = total / n;
    double squares = 0.0;
    for (double v : x) squares += std::pow(v - mean, 2);
    const double variance = squares / (n - 1);
    return jsonObject({
        {"mean", mean},
        {"sd", std::sqrt(variance)},
        {"se", std::sqrt(variance / n)},
    });
}

int main() {
    std::cout << toJson(lesson076()) << '\n';
    return 0;
}

// Fintech Math Bootcamp · Lesson 076 of 120
// Standard Error
// Module 08: Sampling, Estimation, and Statistical Inference
//
// Scenario: Measuring uncertainty in a mean rather than variation among payments
// Rule:     estimated SE(mean) = sample SD / √n
//
// Try it:   Which is the larger number here: sample SD or mean SE?
//
// Lesson article: https://thefintechbuilder.com/financial-mathematics-statistics-and-data-foundations/sampling-estimation-and-statistical-inference/standard-error/
// Free course:    https://courses.thefintechbuilder.com
// Synthetic teaching example, not financial advice or a production library.

/// A minimal JSON value, enough to print this lesson's result.
#[allow(dead_code)]
enum Json {
    Null,
    Bool(bool),
    Num(f64),
    Str(String),
    Arr(Vec<Json>),
    Obj(Vec<(String, Json)>),
}

#[allow(dead_code)]
impl Json {
    fn obj(fields: Vec<(&str, Json)>) -> Json {
        Json::Obj(fields.into_iter().map(|(k, v)| (k.to_string(), v)).collect())
    }

    fn nums(values: &[f64]) -> Json {
        Json::Arr(values.iter().map(|&v| Json::Num(v)).collect())
    }

    /// Pretty-prints with two-space indentation.
    fn pretty(&self, indent: &str) -> String {
        let inner = format!("{}  ", indent);
        match self {
            Json::Null => "null".to_string(),
            Json::Bool(b) => b.to_string(),
            Json::Num(x) => format_number(*x),
            Json::Str(s) => quote(s),
            Json::Arr(items) if items.is_empty() => "[]".to_string(),
            Json::Obj(fields) if fields.is_empty() => "{}".to_string(),
            Json::Arr(items) => {
                let body: Vec<String> = items
                    .iter()
                    .map(|v| format!("{}{}", inner, v.pretty(&inner)))
                    .collect();
                format!("[\n{}\n{}]", body.join(",\n"), indent)
            }
            Json::Obj(fields) => {
                let body: Vec<String> = fields
                    .iter()
                    .map(|(k, v)| format!("{}{}: {}", inner, quote(k), v.pretty(&inner)))
                    .collect();
                format!("{{\n{}\n{}}}", body.join(",\n"), indent)
            }
        }
    }
}

fn format_number(x: f64) -> String {
    if !x.is_finite() {
        "null".to_string()
    } else if x == x.trunc() && x.abs() < 1e15 {
        format!("{}", x as i64)
    } else {
        format!("{}", x)
    }
}

fn quote(s: &str) -> String {
    let mut out = String::from("\"");
    for c in s.chars() {
        match c {
            '"' => out.push_str("\\\""),
            '\\' => out.push_str("\\\\"),
            '\n' => out.push_str("\\n"),
            c => out.push(c),
        }
    }
    out.push('"');
    out
}

fn lesson_076() -> Json {
    let x = [2.0_f64, 3.0, 3.0, 4.0, 4.0];
    let n = x.len() as f64;
    let mean = x.iter().fold(0.0_f64, |s, v| s + v) / n;
    let variance: f64 = x.iter().fold(0.0_f64, |s, v| s + (v - mean).powf(2.0)) / (n - 1.0);
    Json::obj(vec![
        ("mean", Json::Num(mean)),
        ("sd", Json::Num(variance.sqrt())),
        ("se", Json::Num((variance / n).sqrt())),
    ])
}

fn main() {
    println!("{}", lesson_076().pretty(""));
}

// Fintech Math Bootcamp · Lesson 076 of 120
// Standard Error
// Module 08: Sampling, Estimation, and Statistical Inference
//
// Scenario: Measuring uncertainty in a mean rather than variation among payments
// Rule:     estimated SE(mean) = sample SD / √n
//
// Try it:   Which is the larger number here: sample SD or mean SE?
//
// Lesson article: https://thefintechbuilder.com/financial-mathematics-statistics-and-data-foundations/sampling-estimation-and-statistical-inference/standard-error/
// Free course:    https://courses.thefintechbuilder.com
// Synthetic teaching example, not financial advice or a production library.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.Json;

var options = new JsonSerializerOptions { WriteIndented = true };
Console.WriteLine(JsonSerializer.Serialize(Lesson076(), options));

static object Lesson076()
{
    double[] x = { 2, 3, 3, 4, 4 };
    double mean = x.Aggregate(0.0, (s, v) => s + v) / x.Length;
    double variance = x.Aggregate(0.0, (s, v) => s + Math.Pow(v - mean, 2)) / (x.Length - 1);
    return new
    {
        mean,
        sd = Math.Sqrt(variance),
        se = Math.Sqrt(variance / x.Length),
    };
}