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CSE 163

Dissolve and Joins

��Hunter Schafer

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💬Before Class: Are you a cat person or a dog person?

🎵Music: Sammy Rae & The Friends

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Geopandas

  • Exactly like pandas, but with some extra features for geo data
  • Types
    • GeoDataFrame
    • GeoSeries

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import geopandas as gpd

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df = gpd.read_file('data_File.shp')

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df.plot(column='some_col', legend=True)

plt.savefig('plot.png')

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Matplotlib

  • Before, we were using a lot of matplotlib stuff blindly
  • Default plots gets plotted on a global figure (think canvas)
    • Multiple plots would overwrite each other
  • You have to do extra work to get more information on the same set of axes.

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fig, ax = plt.subplots(1)

<plot1>(ax=ax)

<plot2>(ax=ax)

fig.savefig('plot.png')

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Dissolve

  • Exactly the same as a groupby for the the regular columns
    • For the geometry columns, overlays all of the geometries
  • Options for aggfunc
    • ‘first’
    • ‘last’
    • ‘min’
    • ‘max’
    • ‘sum’
    • ‘mean’
    • ‘median’

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Join

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tas.merge(grading, left_on='ta_id',

right_on='grader_id')

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ta_name

ta_id

Ryan

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James

2

Nicole

3

grader_id

student_name

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Flora

3

Paul

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Wen

3

Andrew

ta_name

ta_id

grader_id

student_name

Ryan

1

1

Wen

James

2

2

Flora

Nicole

3

3

Paul

Nicole

3

3

Andrew

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Types of Join

There are interesting questions of what happens if there are rows that don’t “line up”. Different type of joins differ in how to handle this case.

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Types of Joins

left.merge(right, left_on=’lcol’, right_on=’rcol’,

how=’type’)

  • Inner (default): Both values must be present
  • Left: If a value from left has no match, add NaNs
  • Right: If a value from right has no match, add NaNs
  • Outer: If a value from either table has no match, add NaNs

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Hurricane Florence

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Group Work:

Best Practices

When you first working with this group:

  • Introduce yourself!
  • If possible, angle one of your screens so that everyone can discuss together

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Tips:

  • Starts with making sure everyone agrees to work on the same problem
  • Make sure everyone gets a chance to contribute!
  • Ask if everyone agrees and periodically ask each other questions!
  • Call TAs over for help if you need any!

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