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Lecture 9

Functions

DATA 8

Fall 2017

Slides created by John DeNero (denero@berkeley.edu) and Ani Adhikari (adhikari@berkeley.edu)

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Announcements

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Attendance

bit.ly/attend8

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Comparing Histograms

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Overlaid Graphs

For visually comparing two populations

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(Demo)

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Discussion Question

This histogram describes a year of daily temperatures

Try to answer these questions:

  • What proportion of days had a high temp in the range 60-69?
  • What proportion had �a low of 45 or more?
  • How many days had�a difference of more�than 20 degrees�between their high &�low temperatures?

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Defining Functions

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Def Statements

User-defined functions give names to blocks of code

def spread(values):

return max(values) - min(values)

(Demo)

Name

Argument names (parameters)

Body

Return expression

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Discussion Question

What does this function do? What kind of input does it take? What output will it give? What's a reasonable name?

def f(s):

return np.round(s / sum(s) * 100, 2)

(Demo)

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Apply

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Apply

The apply method creates an array by calling a function on every element in input column(s)

  • First argument: Function to apply
  • Other arguments: The input column(s)

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table_name.apply(function_name, 'column_label')

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(Demo)

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Example: Prediction

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Sir Francis Galton

  • 1822 - 1911 (knighted in 1909)
  • A pioneer in making predictions
  • Particular interest in heredity
  • Charles Darwin's half-cousin

(Demo)