Shun-Lung Chang slchangtw

slchangtw / read_files_in_s3

Created October 29, 2020 09:48

	import boto3
	import pandas as pd


	def read_s3(bucket, prefix):
	s3 = boto3.resource("s3")
	bucket = s3.Bucket(bucket)
	prefix_objs = bucket.objects.filter(Prefix=prefix)

	df = pd.concat([pd.read_excel(obj.get()["Body"].read()) for obj in prefix_objs])

slchangtw / tree_implementation

Created January 6, 2019 04:06

slchangtw / fill_zeros

Last active August 13, 2018 10:29

Filling zeros in time series data

	import numpy as np
	import pandas as pd

	from datetime import datetime

	# make an example
	np.random.seed(0)

	item = np.random.choice(['A', 'B'], 10)
	year = np.random.choice([2016, 2017], 10)

slchangtw / Performing PCA through Diagonalization in R

Last active January 25, 2018 10:32

	iris2 <- as.matrix(iris[, 1:4])

	# cetralize data
	centered_iris2 <- scale(iris2, center = TRUE, scale = FALSE)

	# covariance matrix
	cov_iris2 <- (t(centered_iris2) %*% centered_iris2) / (dim(centered_iris2)[1] - 1)
	# perform eigendecomposition on covariance matrix
	eig_cov <- eigen(cov_iris2)

slchangtw / ad_example

Created May 27, 2017 11:13

	from ad import adnumber
	from ad import admath
	import numpy as np

	# ref: http://cs231n.github.io/optimization-2/
	w = adnumber(np.array([2, -3, -3]))
	x = adnumber(np.array([-1, -2, 1]))

	f = 1 / (1 + admath.exp(-sum(w * x)))

slchangtw / adaboost_example.py

Created April 22, 2017 12:04

This example shows how adaboost works

	#!usr/bin/env python3
	# -- coding: utf-8 --

	import numpy as np

	def get_alpha(error):
	return 0.5 * np.log((1 - error) / error)
	def update_weights(y, weights, g, alpha):
	return weights * np.exp(-alpha * g * y) / sum(weights * np.exp(-alpha * g * y))

slchangtw / itertools_notes.py

Created April 22, 2017 11:51

itertools (python)

	#!usr/local/env python3
	# -- coding: utf-8 --

	import itertools

	def consonant(c):
	return c.lower() not in "aeiou"
	# (built-in) filter()
	list(filter(consonant, 'Aartttik'))
	list(itertools.filterfalse(consonant, 'Aartttik'))