CSci 127: Introduction to Computer Science

hunter.cuny.edu/csci

CSci 127 (Hunter) Lecture 7 21 March 2018 1 / 26

Announcements

Next Week: OpenData Showcase: 28 March,4:30-6pm (rescheduled due to snow).

Each lecture includes a survey of computingresearch and tech in NYC.

Today: Mitsue IwataNYC OpenData InitiativeMayor’s Office

Frequently Asked QuestionsFrom lecture slips & recitation sections.

I didn’t get the tree-based networks from last time!No worries– we’ll talk about it first.

Why do we have design questions (like the tree-based one)?The design questions cover two of the course’s learning objectives: exposure toadvanced computer science topics & problem solving.

Please, more time on circuits/logical expressions/truth tables/decisions!We will do a bit today, but much more in the following weeks.

Why is the schedule of classes and quizzes so crazy?

I Lots of holidays has “our week” now starting on Wednesday.I Spring Break is Friday, 30 March to Sunday, 8 April.I Since we’ll miss 2 Fridays, 11 April will follow Friday schedule.I After spring break, “our week” will start on Thursdays.

I’d like to do more. Any suggestions?

I Hunter has an ACM Chapter & Women in CS clubs.I Tech Meetups: focused on just about everything tech

(both via CUNY and city-wide).I Internships: https://jobs.lever.co/cunyinternships

I didn’t get the tree-based networks from last time!

No worries– we’ll talk about it first.

Why do we have design questions (like the tree-based one)?

The design questions cover two of the course’s learning objectives: exposure toadvanced computer science topics & problem solving.

Please, more time on circuits/logical expressions/truth tables/decisions!

We will do a bit today, but much more in the following weeks.

I Lots of holidays has “our week” now starting on Wednesday.

I Spring Break is Friday, 30 March to Sunday, 8 April.I Since we’ll miss 2 Fridays, 11 April will follow Friday schedule.I After spring break, “our week” will start on Thursdays.

I Lots of holidays has “our week” now starting on Wednesday.I Spring Break is Friday, 30 March to Sunday, 8 April.

I Since we’ll miss 2 Fridays, 11 April will follow Friday schedule.I After spring break, “our week” will start on Thursdays.

I Lots of holidays has “our week” now starting on Wednesday.I Spring Break is Friday, 30 March to Sunday, 8 April.I Since we’ll miss 2 Fridays, 11 April will follow Friday schedule.

I After spring break, “our week” will start on Thursdays.

I Hunter has an ACM Chapter & Women in CS clubs.

I Tech Meetups: focused on just about everything tech(both via CUNY and city-wide).

I Internships: https://jobs.lever.co/cunyinternships

(both via CUNY and city-wide).

I Internships: https://jobs.lever.co/cunyinternships

Today’s Topics

Recap: Tree-based Networks

Introduction to Functions

NYC Open Data

Recap: Tree-Based Networks

Haekel List et al., 2013 Network Highlighted Tree

Evolutionary history can be represented by a tree.

Events like hybridization can cause non-tree-like networks.

Is there a tree on which the network is based?That is, can you start with a tree and only add lines between theoriginal tree edges.

Tree-based Networks: Lecture Slip

List et al., 2013

When is the network just a tree with edges joining its branches?

Input: A network.

Output: True if the network is tree-based, and false otherwise.

Design:

I Need paths that connect the “root” to the leaves (with no cycles).I Start by highlighting all edges that must be part of the tree.I Then figure out which edges can’t be there and mark those.I What’s left: a bunch of choices on which edge to include in the treeI Becomes a logic puzzle: a logical expression that can be solved.

List et al., 2013

Input: A network.

Design:

List et al., 2013

Input: A network.

Design:

List et al., 2013

Input: A network.

Design:

List et al., 2013

Input: A network.

Design:

I Need paths that connect the “root” to the leaves (with no cycles).

I Start by highlighting all edges that must be part of the tree.I Then figure out which edges can’t be there and mark those.I What’s left: a bunch of choices on which edge to include in the treeI Becomes a logic puzzle: a logical expression that can be solved.

List et al., 2013

Input: A network.

Design:

I Need paths that connect the “root” to the leaves (with no cycles).I Start by highlighting all edges that must be part of the tree.

I Then figure out which edges can’t be there and mark those.I What’s left: a bunch of choices on which edge to include in the treeI Becomes a logic puzzle: a logical expression that can be solved.

List et al., 2013

Input: A network.

Design:

I Need paths that connect the “root” to the leaves (with no cycles).I Start by highlighting all edges that must be part of the tree.I Then figure out which edges can’t be there and mark those.

I What’s left: a bunch of choices on which edge to include in the treeI Becomes a logic puzzle: a logical expression that can be solved.

List et al., 2013

Input: A network.

Design:

I Need paths that connect the “root” to the leaves (with no cycles).I Start by highlighting all edges that must be part of the tree.I Then figure out which edges can’t be there and mark those.I What’s left: a bunch of choices on which edge to include in the tree

I Becomes a logic puzzle: a logical expression that can be solved.

List et al., 2013

Input: A network.

Design:

Example: Tree-Based Networks

First, highlight what must/mustnot be there.

Then, what’s left: can have edgex if edge y isn’t there (and viceversa):

(x and not y) or (not x and y)

Solve the resulting logical puzzle.

Functions

Functions are a way to break code into pieces,that can be easily reused.

Many languages require that all code must beorganized with functions.

The opening function is often called main()

You call or invoke a function by typing its name,followed by any inputs, surrounded by parenthesis:Example: print("Hello", "World")

Can write, or define your own functions,which are stored, until invoked or called.

Functions

You call or invoke a function by typing its name,followed by any inputs, surrounded by parenthesis:

Example: print("Hello", "World")

Functions

Can write, or define your own functions,

which are stored, until invoked or called.

Functions

“Hello, World!” with Functions

Python Tutor

(Demo with pythonTutor)

In Pairs or Triples:

1. Predict what the code will do: 2. Fill in the missing code:

Python Tutor

(Demo with IDLE)

Predict what the code will do:

(Demo with IDLE)

Recap: Functions

You call or invoke a function by typing its name,followed by any inputs, surrounded by parenthesis:

Recap: Functions

Predict what the code will do:

Python Tutor

Accessing Structured Data: NYC Open Data

Freely available source of data.

Maintained by the NYC data analytics team.

We will use several different ones for this class.

Will use pandas, pyplot & folium libraries to analyze, visualize andmap the data.

Lab 7 covers accessing and downloading NYC OpenData datasets.

Structured Data

Common to have data structured in a spread sheet.

The text file version is called CSV for comma separated values.

Each row is a line; columns are separated by commas.

We will use the popular Python Data Analysis Library (Pandas).

To use, add to the top of your file:

import pandas as pd

To read in a CSV file:myVar = pd.read csv("myFile.csv")

Structured Data

import pandas as pd

Structured Data

import pandas as pd

Structured Data

import pandas as pd

Structured Data

import pandas as pd

Structured Data

import pandas as pd

Example: Reading in CSV Files

nycHistPop.csv

In Lab 6

import matplotlib.pyplot as plt

import pandas as pd

pop = pd.read csv(’nycHistPop.csv’,skiprows=5)

pop.plot(x="Year")

plt.show()

nycHistPop.csv

In Lab 6

import pandas as pd

pop.plot(x="Year")

plt.show()

nycHistPop.csv

In Lab 6

import pandas as pd

pop.plot(x="Year")

plt.show()

nycHistPop.csv

In Lab 6

import pandas as pd

pop.plot(x="Year")

plt.show()

nycHistPop.csv

In Lab 6

import pandas as pd

pop.plot(x="Year")

plt.show()

Series in Pandas

Series can store a column or row of aDataFrame.

Example: pop["Manhattan"] is the Seriescorresponding to the column of Manhattandata.

Example:print("The largest number living in

the Bronx is", pop["Bronx"].max())

Series in Pandas

CS Survey: Mitsue Iwata, Data Analytics

Project Manager, NYC Mayor’s Office of Data Analytics

Hunter College, Class of 2014.

MS, Computational Analysis & Public Policy,University of Chicago, 2016.

Design Question

Design an algorithm that uses NYC OpenData collision data and computesthe closest collision to the location the user provides.(Design only the pseudocode.)

Design Question

Design an algorithm that uses NYC OpenData collision data and computesthe closest collision to the location the user provides.(Design only the pseudocode.)

Design Question

Design an algorithm that uses NYC OpenData collision data and computesthe closest collision to the location the user provides.

How to approach this:

Create a “To Do” list of what your program has to accomplish.

Read through the problem, and break it into “To Do” items.

Don’t worry if you don’t know how to do all the items you write down.

Example:

1 Find data set (great place to look: NYC OpenData).2 Ask user for current location.3 Open up the CSV file.4 Check distance to each to user’s location.5 Save the location with the smallest distance.

Design Question

Example:

Design Question

Example:

Design Question

Example:

Design Question

Example:

Design Question

Example:

1 Find data set (great place to look: NYC OpenData).

2 Ask user for current location.3 Open up the CSV file.4 Check distance to each to user’s location.5 Save the location with the smallest distance.

Design Question

Example:

1 Find data set (great place to look: NYC OpenData).2 Ask user for current location.

3 Open up the CSV file.4 Check distance to each to user’s location.5 Save the location with the smallest distance.

Design Question

Example:

1 Find data set (great place to look: NYC OpenData).2 Ask user for current location.3 Open up the CSV file.

4 Check distance to each to user’s location.5 Save the location with the smallest distance.

Design Question

Example:

1 Find data set (great place to look: NYC OpenData).2 Ask user for current location.3 Open up the CSV file.4 Check distance to each to user’s location.

5 Save the location with the smallest distance.

Design Question

Example:

On lecture slip, write down a topic youwish we had spent more time (and why).

Functions are a way to break code intopieces, that can be easily reused.

You call or invoke a function by typingits name, followed by any inputs,surrounded by parenthesis:Example: print("Hello", "World")

Accessing Formatted Data: NYCOpenData

You call or invoke a function by typingits name, followed by any inputs,surrounded by parenthesis:

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