Chris Wen's Blog

Handling Categorical DataRepresenting Categorical DataTwo common ways to represent a categorical variable with k distinct levels is by storing it as: a vector of strings, a vector of integers between 0 (inclusive) and k (exclusive). 12345678import numpy as npcountries = np.loadtxt("https://raw.githubusercontent.com/gagolews/" + "teaching-data/master/marek/37_pzu_warsaw_marathon_country.txt", dtype="str")x = countries[:16]xnp.unique(x) Encoding and Decodin...

Inspecting the Distribution of Numberic Data12345import numpy as npheights = np.loadtxt("https://raw.githubusercontent.com/gagolews/" + "teaching-data/master/marek/nhanes_adult_female_height_2020.txt")np.random.choice(heights, 24, replace=False) Histograms1234567import matplotlib.pyplot as pltimport seaborn as snsplt.style.use("seaborn")sns.__version__ # FYIsns.histplot(heights, bins=11)plt.show() 1234income = np.loadtxt("https://raw.githubusercontent.co...

Descriptive Statistic fopr Continuous DataHistograms are based on binned data and hence provide us with snapshots of how much probability mass is allocated in diferent parts of the data domain. 1234567import numpy as npincome = np.loadtxt("https://raw.githubusercontent.com/gagolews/" + "teaching-data/master/marek/uk_income_simulated_2020.txt")b = [0, 10000, 20000, 30000, 40000, 50000, 60000, 80000, np.inf] # bin boundsc = np.histogram(income, bins=b)[0] # countsfor i ...

Basic Usage of Data AnalysisGetting Started with JupyterLabJupyterLab is a web-based development environment supporting numerous programming languages, including, of course, Python. jupyterlab Scalar Types in PythonBasic Operations on Data Framesdoc pre-requisite123import numpy as npimport pandas as pdpd.set_option("display.notebook_repr_html", False) # disable "rich" output Aggregating1234567891011121314151617181920np.random.seed(123)d = pd.DataFrame(dict( u = np.roun...

Connecting Prisma application to Supabase PostgresCreste a custom user fro Prismacreate a Prisma DB user with full privileges on the public schema123456789101112131415-- Create custom usercreate user "prisma" with password 'custom_password' bypassrls createdb;-- extend prisma's privileges to postgres (necessary to view changes in Dashboard)grant "prisma" to "postgres";-- Grant it necessary permissions over the relevant schemas (public)grant usage o...

DescriptionGiven two strings s and t, determine if they are isomorphic. Two strings s and t are isomorphic if the characters in s can be replaced to get t. All occurrences of a character must be replaced with another character while preserving the order of characters. No two characters may map to the same character, but a character may map to itself. Approach12345678910111213141516class Solution: def isIsomorphic(self, s: str, t: str) -> bool: char_index_s = {} c...

DescriptionGiven two strings s and t, return true if s is a subsequence of t, or false otherwise.A subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e., “ace” is a subsequence of “abcde” while “aec” is not). Example 1: 12Input: s = "abc", t = "ahbgdc"Output: true Example 2: 12Input: s = "axc", t = "ahbgdc&qu...

Interview QuestionsCore Java (OOPs, Collections, Concurrency Basics)Explain difference between HashMap, HashTable, and ConcurrentHashMap. Feature HashMap Hashtable ConcurrentHashMap Thread Safety Not thread-safe Thread-safe (synchronized methods) Thread-safe (lock segmentation / fine-grained locking) Null Keys/Values Allows one null key and multiple null values Does not allow any null keys/values Does not allow null keys/values Performance Faster (no synchronization overhead) Slowe...

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Question 1: Concurrent Web Crawler ImplementationDesign and implement a multi-threaded web crawler that efficiently crawls a specific domain and counts unique URLs Requirements: Handle circular references and invalid URLs implement rate limiting and exponential back off Process robots.txt compliance Support different URL schemes and redirects Optimize for memory usage with large datasets Overview12345678910111213141516171819[Seed URLs] | [Frontier in-memory queue] <--- [Persistent ov...