145 lines
2.5 KiB
Markdown
145 lines
2.5 KiB
Markdown
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# Grammar of Graphics with Altair
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## CAPP 30239
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---
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## Today
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- Grammar of Graphics
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- Types of Data
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- Intro to Altair
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---
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## Grammar of Graphics
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Hadley Wickham, creator of `ggplot2` and `tidyverse`, ["A Layered Grammar of Graphics"](http://vita.had.co.nz/papers/layered-grammar.pdf).
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Key Idea: move beyond pre-defined composites like "scatter plot" and "bar chart" into a composable grammar from which we can construct a wide variety of visualizations.
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---
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## Wickham's Components:
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1. data and aesthetic mappings,
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2. one or more layers, each with
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- a geometric object (line, point, etc.)
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- (optional) statistical transformation
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- (optional) position adjustment
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3. one scale per aesthetic mapping (color, size, etc.)
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4. a coordinate system
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5. facet specification
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---
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## Types of Data
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### **N** - Nominal
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"strings" with no **order** (alphabetical does not count)
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Species
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States
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Countries
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### **O** - Ordered
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- Grades: A, B, C, D, E, F
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- Rankings: 1st, 2nd, 3rd
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---
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## Types of Data (Quantitative)
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### **Q** - Interval (arbitrary zero)
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- Dates (1 CE, Jan 1 1970, or...)
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- Location (lat, lon)
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Only differences matter, can't compare ratios.
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_(What is 2024 / 1990?)_
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### **T**emporal
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Some systems (like Altair) will also offer this option specifically for dates and times.
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### **Q** - Ratio (zero fixed)
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Physical measurements, counts, amounts.
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"4 km is _twice as far_ as 2 km"
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---
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## Types of Data (Operations)
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| | =, != | <, >, <=, >= | +, - | ÷ |
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| -------- | ----- | ------------ | ---- | --- |
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| Nominal | ✓ | | | |
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| Ordered | ✓ | ✓ | | |
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| Interval | ✓ | ✓ | ✓ | |
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| Ratio | ✓ | ✓ | ✓ | ✓ |
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---
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## Data Model to N, O, Q
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- string?
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- bool?
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- float/int?
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Possible exceptions?
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---
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## Data Model to N, O, Q
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_Typically:_
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- string - nominal or ordered
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- bool - nominal
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- float/int - interval or ratio
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Possible Exceptions?
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- Numeric IDs
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- ZIP Codes
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- ratio data stored with units (e.g. "10km")
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---
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## Mapping of Variables to Aesthetics
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- position (X, Y, Z)
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- length
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- angle
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- slope
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- area
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- volume
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- density
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- hue
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- saturation
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- texture
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- connection
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- containment/grouping
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- shape
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---
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### Mackinlay's "effectiveness"
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---
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## Altair's Grammar
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Altair condenses several of the different pieces of the grammar to _"encoding channels"_.
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We've seen X, Y, and color, let's take a look at some examples of other encoding channels.
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---
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