Lecture 12

Table Examples

DATA 8

Spring 2020

Weekly Goals

• Monday
• No class

​

• Today
• Table review
• Table examples
• Friday
• Conditionals and iteration
• Simulation

​

Review: Pivot and Join

Pivot

• Cross-classifies according to two categorical variables
• Produces a grid of counts or aggregated values
• Two required arguments:
• First: variable that forms column labels of grid
• Second: variable that forms row labels of grid
• Two optional arguments (include both or neither)
• values=’column_label_to_aggregate’
• collect=function_to_aggregate_with

(Demo)

Group or Pivot?

Grouped Table

• One combo of grouping variables per row
• Any number of grouping variables
• Aggregate values of all other columns in table
• Missing combos absent

Pivot Table

• One combo of grouping variables per entry
• Two grouping variables: columns and rows
• Aggregate values of values column
• Missing combos = 0�(or empty string)

For cross-classification:

Joining Two Tables

drinks

discounts

drinks.join('Cafe', discounts, 'Location')

Match rows in this table ...

… using values in this column ...

… with rows in that table ...

… using values in that column.

The joined column is sorted automatically

Important Table Methods

t.select(column, …) or t.drop(column, …)

t.take([row_num, …]) or t.exclude([row_num, …])

t.sort(column, descending=False, distinct=False)

t.where(column, are.condition(...))

t.apply(function_name, column, …)

t.group(column) or t.group(column, function_name)

t.group([column, …]) or t.group([column, …], function_name)

t.pivot(cols, rows) or t.pivot(cols, rows, vals, function_name)

t.join(column, other_table, other_table_column)

http://data8.org/sp20/python-reference.html

Examples