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Lecture 9

Functions

DATA 8

Spring 2024

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Announcements

  • HW 3 due Wednesday at 5pm
  • Lab 4 due Friday
  • Project 1 will be released on Friday
  • HW 1 regrade requests are due Wednesday
  • My OH are also on Zoom today 4-6pm

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Histograms

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Area and Height

Area of bar = % in bin = Height x width of bin

  • “How many individuals in the bin?” Use area.

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  • “How crowded is the bin?” Use height.

(Demo)

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Charts Wrap Up

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Summary

  • Line graph: sequential data (over time, etc.)�
  • Scatter plot: relation between two numerical variables

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  • Bar chart: distribution of one categorical variable or relation between a categorical and a numerical variable

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  • Histogram: distribution of one numerical variable

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(Demo)

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Discussion Question

You have data about daily temperatures as shown. Which type of chart would show the answer to each question?

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  • Are there more cloudy than�sunny days?
  • What percentage of days�have a high at least 72º?
  • Do days with hotter highs �tend to have hotter lows?

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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

apply

  1. Calls a function on every element in the input column(s)
  2. Produces an array containing the output of the function on each input column element.
  3. First argument: Function to apply
  4. Other arguments: Specified input column(s)

table_name.apply(function_name, 'column_label(s)')

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(Demo)