---
title: "Network Graphs"
author: "Prof. Eric A. Suess"
date: "March 24, 2021"
output:
  beamer_presentation: default
  ioslides_presentation: default
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = FALSE)
```

## Visualizing a network of bigrams

Network graphs can be used to visualize bigrams in text data.

Network graphs are constructed using

- **from:** the node an edge is coming from
- **to:** the note an edge is going towards
- **weight:** A numeric value associated with each edge

## The *igraph* R package

The *igraph* R package has a function that can convert a tidy data frame into a set of "from", "to" nodes with edges.  

     > graph_from_data_frame()
     
Note that this function does not make a plot!  This function makes the **graph** that can be plotted.

The authors discuss *polishing* the plot with arrows and words.

## Markov chain 

There is a reference in the book that a plot of a network graph is a visualization of a Markov chain.  This model assumes there is only a one step dependence.  This is what bigrams look at.

##  Advanced Book 

[Speech and Language Processing](https://web.stanford.edu/~jurafsky/slp3/ed3book.pdf)  

This is a bit more advanced book.  

In Chapter 3 there is a very nice presentation of n-grams 

In Chapter 4 there is a very nice presentation of naive Bayes.