Calculate Standard Deviation (Continuous Series)

actual_and_assumed.py

# Calculate Standard Deviation (Continuous Series | Actual & Assumed Mean Methods)

# Simple python program I wrote to automate a huge portion of my homework.
# Economics is a nightmare :√

from prettytable import PrettyTable
def number(num):
	"""Returns any string containing number (int/float) in a cleaner way."""
	#num = str(round(float(num), 2))
	return num[:num.rindex('.')] if num.endswith('.0') else num

def get_input(prompt):
	"""Function to collect input from the user in two different ways."""
	_a = []
	print(prompt)
	while True:
		_i = input(">> ").strip()
		if ',' in _i:
			_a = _i.replace(' ', '').split(',')
			break
		elif not _i:
			break
		else:
			_a.append(_i)
	return _a

X = get_input("Enter X (individually or comma separated):")
print()
f = get_input("Enter F (individually or comma separated):")
print()
# Test Values
#X = ['0-5', '5-10', '10-15', '15-20', '20-25', '25-30', '30-35', '35-40']
#f = ['2', '5', '7', '13', '21', '16', '8', '3']

if len(X) != len(f):
	print("Error: Number of items do not match.")
	
print("(1) Actual Mean Method | (2) Assumed Mean Method")
method = input(">> ").strip()

if method in {'2', 'assumed'}:
	# Assumed Mean Method: σ = √(Σfdx2/N - (Σfdx/N)2)
	m = []
	for i in X:
		_nums = i.split('-')
		m.append(number(str(round((int(_nums[0]) + int(_nums[1])) / 2, 2))))

	# Assume a mean value.
	A = m[len(m) // 2]

	dx = [number(str(round(float(i) - float(A), 2))) for i in m] # m - A
	dx2 = [number(str(round(float(i) * float(i), 2))) for i in dx] # d * d
	fdx = [number(str(round(float(_f) * float(_dx), 2))) for _f, _dx in zip(f, dx)] # f * dx
	fdx2 = [number(str(round(float(_f) * float(_dx2), 2))) for _f, _dx2 in zip(f, dx2)] # f * dx2

	Σf = number(str(round(sum(float(i) for i in f), 2)))
	Σfdx = number(str(round(sum(float(i) for i in fdx), 2)))
	Σfdx2 = number(str(round(sum(float(i) for i in fdx2), 2)))

	σ = round(((float(Σfdx2)/float(Σf)) - ((float(Σfdx)/float(Σf)) ** 2)) ** 0.5, 2)
	
	m[len(m) // 2] = f'({A})A'  # little visual indicator for assumed mean

	# Prepare a table to represent the numbers.
	table = PrettyTable(['X', 'f', 'm', 'dx', 'dx2', 'fdx', 'fdx2'])
	for i in range(len(X)):
		table.add_row([X[i], f[i], m[i], dx[i], dx2[i], fdx[i], fdx2[i]])
	table.add_row([' ', '= ' + Σf, ' ', ' ', ' ', '= ' + Σfdx, '= ' + Σfdx2])

	print()
	print(table)
	print()
	# Break down the equations when printing so that it is easier to understand.
	print("σ = √Σfdx2/N - (Σfdx/N)2")
	print(f"\t = √{Σfdx2}/{Σf} - ({Σfdx}/{Σf})2")
	print(f"\t = √{round(float(Σfdx2)/float(Σf), 2)} - ({round(float(Σfdx)/float(Σf), 2)})2")
	print(f"\t = √{round(float(Σfdx2)/float(Σf), 2)} - {round(float(Σfdx)/float(Σf), 2) ** 2}")
	print(f"\t = √{round(float(Σfdx2)/float(Σf), 2) - (round(float(Σfdx)/float(Σf), 2) ** 2)}")
	print(f"\t = {σ}")
else:
	# Actual Mean Method: σ = √(Σfx2/N)
	m = []
	for i in X:
		_nums = i.split('-')
		m.append(number(str(round((int(_nums[0]) + int(_nums[1])) / 2, 2))))  # X1+X2 / 2

	fm = [number(str(round(float(_f) * float(_m), 2))) for _f, _m in zip(f, m)]  # f * m

	Σf = number(str(round(sum(float(i) for i in f), 2)))
	Σfm = number(str(round(sum(float(i) for i in fm), 2)))

	x̄ = round(float(Σfm)/float(Σf), 2) # x̄ = Σfm/Σf

	x = [number(str(round(float(i) - float(x̄), 2))) for i in m]  # x = m - x̄
	x2 = [number(str(round(float(i) * float(i), 2))) for i in x]  # x2 = x * x
	fx2 = [number(str(round(float(_f) * float(_x2), 2))) for _f, _x2 in zip(f, x2)]  # fx2 = f * x2

	Σfx2 = number(str(round(sum(float(i) for i in fx2), 2)))

	σ = round((float(Σfx2) / float(Σf)) ** 0.5, 2)

	# Prepare a table.
	table = PrettyTable(['X', 'f', 'm', 'fm', 'x', 'x2', 'fx2'])
	for i in range(len(X)):
		table.add_row([X[i], f[i], m[i], fm[i], x[i], x2[i], fx2[i]])
	table.add_row([' ', '= ' + Σf, ' ', '= ' + Σfm, ' ', ' ', '= ' + Σfx2])

	print()
	print(table)
	print()
	print("x̄ = Σfm/N")
	print(f"\t = {Σfm}/{Σf}")
	print(f"\t = {x̄}")
	print()
	print("σ = √Σfx2/N")
	print(f"\t = √{Σfx2}/{Σf}")
	print(f"\t = √{round(float(Σfx2) / float(Σf), 2)}")
	print(f"\t = {σ}")
	
# 06-01-2022