9: Dictionaries
- Page ID
- 122394
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)- 9.1: Dictionaries
- This page explains Python dictionaries as data structures that map keys to values, allowing varied key types. Unlike lists, dictionaries permit any data type as keys, forming key-value pairs manipulated through functions and brackets. Item order is unpredictable, but keys can efficiently retrieve corresponding values. The length of a dictionary is obtained using the len function, and the in operator verifies key presence, benefiting from a hash table algorithm for efficiency.
- 9.2: Dictionary as a Set of Counters
- This page outlines three methods for counting letter frequencies in a string: using individual variables, a list, or a dictionary, with a focus on the efficiency of the dictionary method that records only present letters. It provides an example of updating a letter frequency histogram and highlights the use of the `get` method in dictionaries, which simplifies the counting process and reduces code complexity.
- 9.3: Dictionaries and Files
- This page outlines a Python program designed to count word occurrences in a simplified version of "Romeo and Juliet." It explains how to read the file, split lines into words, and tally counts using a dictionary with nested loops. While the program effectively counts words, it presents the results unsorted, making it difficult to identify the most common words. Suggestions for additional coding improvements to enhance output are also provided.
- 9.4: Looping and Dictionaries
- This page explains how to iterate over a Python dictionary using for loops to access keys. It includes examples of printing key-value pairs, filtering entries based on values, and sorting keys alphabetically. The content highlights the unordered nature of dictionary keys and provides insights into retrieving associated values, showcasing common patterns for working with dictionaries in Python.
- 9.5: Advanced Text Parsing
- This page explains how to analyze a text file in Python by removing punctuation and standardizing capitalization. It highlights treating similar words as identical and demonstrates using string methods like `translate` and `lower`. The provided code illustrates reading the file, processing lines, and counting word occurrences, culminating in a dictionary of word counts. The author emphasizes that understanding Python's built-in tools can streamline data analysis tasks.
- 9.6: Debugging
- This page provides strategies for debugging large datasets, including scaling down inputs, printing summaries and data types, implementing self-checks, conducting sanity and consistency checks, and formatting output for clarity. These methods enhance error identification and overall debugging efficiency.
- 9.E: Dictionaries (Exercises)
- This page presents programming exercises that focus on analyzing email log data. The exercises involve counting messages by day of the week using a dictionary, creating a histogram of email addresses to determine message counts, identifying the address with the most messages, and modifying the program to track message counts per domain name instead of full addresses.
- 9.G: Dictionaries (Glossary)
- This page defines key programming terms related to data structures, including dictionaries as key-value pairs and hashtables as their underlying algorithm in Python. It also discusses hash functions for key location, histograms, and other concepts like key-value pairs, keys, values, lookup operations, and nested loops.