Lecture 13

Conditionals and Iteration

DATA 8

Spring 2020

Weekly Goals

• Monday
• No class

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• Wednesday
• Table review
• Table examples
• Today
• Booleans, conditionals, and iteration
• Simulation

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Announcements

Comparison and Booleans

Comparison Operators

The result of a comparison expression is a bool value

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x = 2 y = 3

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x > 1 x > y y >= 3

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x == y x != 2 2 < x < 5

Aggregating Comparisons

Summing an array or list of bool values will count the True values only.

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1 + 0 + 1 == 2

True + False + True == 2

sum([1 , 0 , 1 ]) == 2

sum([True, False, True]) == 2

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(Demo)

Control Statements

Control Statements

These statements control the sequence of computations that are performed in a program

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• The keywords if and for begin control statements

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• The purpose of if is to define functions that choose different behavior based on their arguments

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(Demo)

Random Selection

Random Selection

np.random.choice

• Selects uniformly at random
• with replacement
• from an array,
• a specified number of times

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np.random.choice(some_array, sample_size)

(Demo)

Appending Arrays

A Longer Array

• np.append(array_1, value)
• new array with value appended to array_1
• value has to be of the same type as elements of array_1
• np.append(array_1, array_2)
• new array with array_2 appended to array_1
• array_2 elements must have the same type as array_1 elements

(Demo)

Iteration

for Statements

• for is a keyword that begins a control statement

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• The purpose of for is to perform a computation for every element in a list or array

(Demo)

Optional: Advanced where

A Closer Look at where

t.where(array_of_bool_values)

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returns a table

with only the rows of t for which

the corresponding bool is True.

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(Demo)