---
title: "Introduction to ecodive"
output: rmarkdown::html_vignette
vignette: >
  %\VignetteIndexEntry{Introduction to ecodive}
  %\VignetteEngine{knitr::rmarkdown}
  %\VignetteEncoding{UTF-8}
---


## Introduction

Ecodive calculates ecological diversity metrics. Alpha diversity metrics
provide insight about a single sample's diversity, whereas beta diversity
metrics indicate how different a pair of samples are from each other.

In this guide, we'll use the `ex_counts` dataset included with ecodive.
`ex_counts` is a feature table that enumerates how many times each bacterial
genera was observed on different body sites.

```r
library(ecodive)

t(ex_counts)
#>                   Saliva Gums Nose Stool
#> Streptococcus        162  793   22     1
#> Bacteroides            2    4    2   611
#> Corynebacterium        0    0  498     1
#> Haemophilus          180   87    2     1
#> Propionibacterium      1    1  251     0
#> Staphylococcus         0    1  236     1
```

In this example, the 'features' in our feature table are genera. However, your 
own dataset can use whatever feature makes sense - species, OTUs, ASVs, or 
even something completely unrelated to ecology.



## Alpha Diversity

Alpha diversity metrics describe how many different genera are present in a
sample. Depending on the metric, this can take into account the number of unique
genera (richness), how evenly the population is split among genera (evenness),
or how distantly related the genera are (phylogenetic diversity).

The available alpha diversity metrics can be listed using `list_metrics()`.

```r
list_metrics('alpha')[,1:5]
#>                                        name          id phylo weighted int_only
#> 1  Abundance-based Coverage Estimator (ACE)         ace FALSE     TRUE     TRUE
#> 3                       Berger-Parker Index      berger FALSE     TRUE    FALSE
#> 6                           Brillouin Index   brillouin FALSE     TRUE     TRUE
#> 8                                     Chao1       chao1 FALSE     TRUE     TRUE
#> 15           Faith's Phylogenetic Diversity       faith  TRUE    FALSE    FALSE
#> 16                           Fisher's Alpha      fisher FALSE     TRUE     TRUE
#> 18                       Gini-Simpson Index     simpson FALSE     TRUE    FALSE
#> 23                    Inverse Simpson Index inv_simpson FALSE     TRUE    FALSE
#> 29                Margalef's Richness Index    margalef FALSE     TRUE     TRUE
#> 31                           McIntosh Index    mcintosh FALSE     TRUE     TRUE
#> 32               Menhinick's Richness Index   menhinick FALSE     TRUE     TRUE
#> 37                        Observed Features    observed FALSE    FALSE    FALSE
#> 40                  Shannon Diversity Index     shannon FALSE     TRUE    FALSE
#> 45               Squares Richness Estimator     squares FALSE     TRUE     TRUE
```

* Further reading: `vignette('adiv')`


## Beta Diversity

Beta diversity metrics describe how different two samples are, based on the
genera observed in each.UniFrac metrics incorporate a phylogenetic tree into
this calculation.

The available alpha diversity metrics can be listed using `list_metrics()`.

```r
list_metrics('beta')[,2:6]
#>                           id phylo weighted int_only true_metric
#> 2                  aitchison FALSE     TRUE    FALSE        TRUE
#> 4              bhattacharyya FALSE     TRUE    FALSE        TRUE
#> 5                       bray FALSE     TRUE    FALSE       FALSE
#> 7                   canberra FALSE     TRUE    FALSE        TRUE
#> 9                  chebyshev FALSE     TRUE    FALSE        TRUE
#> 10                     chord FALSE     TRUE    FALSE        TRUE
#> 11                     clark FALSE     TRUE    FALSE        TRUE
#> 12                  sorensen FALSE    FALSE    FALSE       FALSE
#> 13                divergence FALSE     TRUE    FALSE        TRUE
#> 14                 euclidean FALSE     TRUE    FALSE        TRUE
#> 17       generalized_unifrac  TRUE     TRUE    FALSE        TRUE
#> 19                     gower FALSE     TRUE    FALSE        TRUE
#> 20                   hamming FALSE    FALSE    FALSE        TRUE
#> 21                 hellinger FALSE     TRUE    FALSE        TRUE
#> 22                      horn FALSE     TRUE    FALSE       FALSE
#> 24                   jaccard FALSE    FALSE    FALSE        TRUE
#> 25                    jensen FALSE     TRUE    FALSE        TRUE
#> 26                       jsd FALSE     TRUE    FALSE        TRUE
#> 27                lorentzian FALSE     TRUE    FALSE       FALSE
#> 28                 manhattan FALSE     TRUE    FALSE        TRUE
#> 30                  matusita FALSE     TRUE    FALSE        TRUE
#> 33                 minkowski FALSE     TRUE    FALSE        TRUE
#> 34                  morisita FALSE     TRUE     TRUE       FALSE
#> 35                    motyka FALSE     TRUE    FALSE       FALSE
#> 36        normalized_unifrac  TRUE     TRUE    FALSE        TRUE
#> 38                    ochiai FALSE    FALSE    FALSE       FALSE
#> 39                psym_chisq FALSE     TRUE    FALSE       FALSE
#> 40          robust_aitchison FALSE     TRUE    FALSE        TRUE
#> 42                   soergel FALSE     TRUE    FALSE        TRUE
#> 43             squared_chisq FALSE     TRUE    FALSE       FALSE
#> 44             squared_chord FALSE     TRUE    FALSE       FALSE
#> 45         squared_euclidean FALSE     TRUE    FALSE       FALSE
#> 47                    topsoe FALSE     TRUE    FALSE        TRUE
#> 48        unweighted_unifrac  TRUE    FALSE    FALSE        TRUE
#> 49 variance_adjusted_unifrac  TRUE     TRUE    FALSE        TRUE
#> 50               wave_hedges FALSE     TRUE    FALSE       FALSE
#> 51          weighted_unifrac  TRUE     TRUE    FALSE        TRUE
```




## Example

### Rarefaction

The `ex_counts` feature table has 345 saliva observations, but nose has 1011
observations. This unequal sampling depth can cause systematic biases.
Specifically, rare genera will be observed more often in samples with greater
sampling depths, thereby artificially inflating the observed richness.

The first step then is to rarefy `ex_counts` so that all samples have
the same number of observations. Rarefying randomly removes observations from
samples with more observations.


```r
rowSums(ex_counts)
#> Saliva   Gums   Nose  Stool 
#>    345    886   1011    615 

counts <- rarefy(ex_counts)

rowSums(counts)
#> Saliva   Gums   Nose  Stool 
#>    345    345    345    345 

t(counts)
#>                   Saliva Gums Nose Stool
#> Streptococcus        162  309    6     1
#> Bacteroides            2    2    0   341
#> Corynebacterium        0    0  171     1
#> Haemophilus          180   34    0     1
#> Propionibacterium      1    0   82     0
#> Staphylococcus         0    0   86     1
```


### Classic Metrics

These alpha and beta diversity metrics have been around for 50+ years and don't
require a phylogenetic tree. The beta diversity functions can take a `weighted =
FALSE` argument to use only presence/absence information instead of relative
abundances.

```r
## Alpha Diversity -------------------

shannon(counts)
#>     Saliva       Gums       Nose      Stool 
#> 0.74119910 0.35692121 1.10615349 0.07927797 


## Beta Diversity --------------------

bray(counts)
#>          Saliva      Gums      Nose
#> Gums  0.4260870                    
#> Nose  0.9797101 0.9826087          
#> Stool 0.9884058 0.9884058 0.9913043
```


### Phylogenetic Metrics

A phylogenetic tree enables alpha and beta diversity metrics to take into
account evolutionary relatedness between the observed genera, generally giving
higher diversity values for samples with more distantly related genera. Faith
(for alpha diversity) and UniFrac (for beta diversity) are examples of
phylogenetic metrics.

The `ex_tree` object included with ecodive provides the phylogenetic tree for
the genera in `ex_counts`. For your own datasets, you can use ecodive's
`read_tree()` function to import a phylogenetic tree from a newick formatted
string or file.


```r
## Alpha Diversity -------------------

faith(counts, tree = ex_tree)
#> Saliva   Gums   Nose  Stool 
#>    180    155    101    202 


## Beta Diversity --------------------

normalized_unifrac(counts, tree = ex_tree)
#>          Saliva      Gums      Nose
#> Gums  0.4328662                    
#> Nose  0.7928701 0.6767840          
#> Stool 0.9677535 0.9829736 0.9936121
```


### Distance Matrices

Beta diversity functions return a `dist` object. You can convert this to a
standard R matrix with the `as.matrix()` function.

```r
dm <- bray(counts)
dm
#>          Saliva      Gums      Nose
#> Gums  0.1428571                    
#> Nose  0.5000000 0.7142857          
#> Stool 0.3333333 0.2500000 0.3333333

mtx <- as.matrix(dm)
mtx
#>           Saliva      Gums      Nose     Stool
#> Saliva 0.0000000 0.1428571 0.5000000 0.3333333
#> Gums   0.1428571 0.0000000 0.7142857 0.2500000
#> Nose   0.5000000 0.7142857 0.0000000 0.3333333
#> Stool  0.3333333 0.2500000 0.3333333 0.0000000

mtx['Saliva', 'Nose']
#> [1] 0.5
```


## Performance with Large Datasets

`ecodive` is designed to be fast out-of-the-box. However, if you are working
with very large datasets (e.g., thousands of samples), you can gain additional
performance by following the recommendations in our performance guide.

* Further reading: `vignette('performance')`
