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Publish Ch. 26
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‎assets/book/learn_python_with_jupyter.pdf

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‎assets/notebooks/26_dictionary_use.ipynb

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{
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"cells": [
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"# 26. Counting, compressing, and sorting\n",
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"\n",
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"\n",
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"## What are dictionaries for?\n",
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"\n",
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"\n",
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"[Learn Python with Jupyter](https://learnpythonwithjupyter.com/) by [Serena Bonaretti](https://sbonaretti.github.io/) \n",
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"Narrative license: [CC BY-NC-SA](https://creativecommons.org/licenses/by-nc-sa/2.0/) \n",
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"Code license: [GNU-GPL v3](https://www.gnu.org/licenses/gpl-3.0.en.html) "
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"--- \n",
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"## 1. Counting elements"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"- Given the following string:"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"source": [
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"greetings = \"hello! how are you?\""
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"- Create a dictionary where the keys are the letters of the alphabet found in the string, and the corresponding values are the number of times each letter is present. Write the code in two ways: (1) using `if`/`else`, and (2) using `.get()` \n",
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"\n",
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"1. Using `if`/`else`:"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {
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"scrolled": true
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},
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"outputs": [],
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"source": [
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"letter_counter = {}\n",
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"\n",
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"for letter in greetings:\n",
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" if letter not in letter_counter.keys():\n",
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" letter_counter[letter] = 1\n",
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" else:\n",
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" letter_counter[letter] += 1 \n",
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"\n",
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"for k, v in letter_counter.items():\n",
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" print (k, v)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {
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"tags": []
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},
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"source": [
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"2. Using `.get()`:"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"source": [
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"letter_counter = {}\n",
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"\n",
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"for letter in greetings:\n",
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" letter_counter[letter] = letter_counter.get(letter, 0) + 1\n",
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"\n",
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"for k, v in letter_counter.items():\n",
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" print (k, v) "
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"---\n",
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"## 2. Compressing information"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"- Given the following list:"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"source": [
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"sparse_vector = [0,0,0,1,0,7,0,0,4,0,0,0,8,0,0,0,6,0,0,0,0,0,0,0,9,0,0]"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"- Convert it into a dictionary:"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"source": [
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"# create the dictionary\n",
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"sparse_dict = {}\n",
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"for i in range(len(sparse_vector)):\n",
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" if sparse_vector[i] != 0:\n",
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" sparse_dict[i] = sparse_vector[i]\n",
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"\n",
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"# save the list length \n",
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"sparse_dict[\"length\"] = len(sparse_vector) \n",
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" \n",
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"# print\n",
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"for k,v in sparse_dict.items():\n",
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" print (k,v) "
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"- How do we get back to the sparse vector? "
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"source": [
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"# create a list of zeros\n",
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"sparse_vector_back = [0] * sparse_dict[\"length\"]\n",
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"\n",
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"# add nonzero values\n",
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"for k,v in sparse_dict.items():\n",
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" if k != \"length\":\n",
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" sparse_vector_back[k] = v \n",
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"\n",
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"# print\n",
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"print (sparse_vector_back)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"---\n",
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"## 3. Sorting dictionary"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"- Given the following dictionary:"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"source": [
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"registry = {\"Shaili\":4, \"Chris\":90, \"Maria\":70}"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"- Sort the dictionary items according to their *keys*:"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"source": [
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"# create a new dictionary\n",
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"sorted_registry= {}\n",
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"\n",
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"# sort the keys\n",
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"sorted_keys = list(registry.keys())\n",
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"sorted_keys.sort()\n",
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"\n",
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"# fill out the new dictionary\n",
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"for k in sorted_keys:\n",
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" sorted_registry[k] = registry[k]\n",
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" \n",
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"print (sorted_registry)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"- Sort the dictionary items according to their *values*:"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"source": [
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"# create a new dictionary\n",
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"sorted_registry = {}\n",
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"\n",
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"# sort keys according to values \n",
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"sorted_keys = sorted(registry, key=registry.get) \n",
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"\n",
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"# fill out the new dictionary\n",
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"for k in sorted_keys:\n",
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" sorted_registry[k] = registry[k]\n",
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" \n",
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"print (sorted_registry)"
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]
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}
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],
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"metadata": {
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"kernelspec": {
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"display_name": "Python 3 (ipykernel)",
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"language": "python",
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"name": "python3"
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},
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"language_info": {
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"codemirror_mode": {
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"name": "ipython",
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"version": 3
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},
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"file_extension": ".py",
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"mimetype": "text/x-python",
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"name": "python",
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"nbconvert_exporter": "python",
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"pygments_lexer": "ipython3",
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"version": "3.11.7"
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},
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"widgets": {
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"application/vnd.jupyter.widget-state+json": {
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"state": {},
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"version_major": 2,
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"version_minor": 0
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}
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}
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},
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"nbformat": 4,
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"nbformat_minor": 4
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}

‎index.html

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<div class="col-lg-12">
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<div class="progress">
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<span class="skill">BOOK COMPLETION <i class="val">68%</i></span>
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<span class="skill">BOOK COMPLETION <i class="val">70%</i></span>
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<div class="progress-bar-wrap">
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<div class="progress-bar" role="progressbar" aria-valuenow="68" aria-valuemin="0" aria-valuemax="100"></div>
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<div class="progress-bar" role="progressbar" aria-valuenow="70" aria-valuemin="0" aria-valuemax="100"></div>
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</div>
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</div>
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<center>Next upload: <b>Chapter 26</b> on <b>April 24</b> </center>
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<center>Next upload: <b>Chapter 27</b> on <b>June 23</b> </center>
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</div>
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</div>
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<ol start="24">
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<a href="assets/notebooks/24_dictionaries.ipynb" onclick="download" ><li>Inventory at the English bookstore<br> <i>Dictionaries</i></li></a>
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<a href="assets/notebooks/25_dictionary_list.ipynb" onclick="download" ><li>Trip to Switzerland<br> <i>Dictionaries with lists as values</i></li></a>
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<li>Counting, compressing, and sorting<br> <i>Dictionary use cases</i></li>
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<a href="assets/notebooks/26_dictionary_use.ipynb" onclick="download" ><li>Counting, compressing, and sorting<br> <i>What are dictionaries for?</i></li></a>
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<li>Overview of strings<br> <i>Operations, methods, and tricks</i></li>
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</ol>
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</div>

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