# Introduction to the taxa package

#### Scott Chamberlain and Zachary Foster

#### 2020-02-24

`taxa` defines taxonomic classes and functions to manipulate them. The goal is to use these classes as low level fundamental taxonomic classes that other R packages can build on and supply robust manipulation functions (e.g. subsetting) that are broadly useful.

There are two distinct types of classes in `taxa`:

- Classes that are concerned only with taxonomic information: `taxon`, `taxonomy`, `hierarchy`, etc.
- A class called `taxmap` that is concerned with combining taxonomic data with user-defined data of any type (e.g. molecular sequences, abundance counts etc.)

Diagram of class concepts for `taxa` classes:

Relationship between classes implemented in the taxa package. Diamond-tipped arrows indicate that objects of one class are used in another class. For example, a database object can stored in the taxon_rank, taxon_name, or taxon_id objects. A standard arrow indicates inheritance. For example, the taxmap class inherits the taxonomy class. `*` means that the object (e.g. a database object) can be replaced by a simple character vector. `?` means that the data is optional (Note: being able to replace objects with characters might be going away soon).

## Install

For the latest “stable” release, use the CRAN version:

    install.packages("taxa")

For all the latest improvements, bug fixes, and bugs, you can download the development version:

    devtools::install_github("ropensci/taxa")

    library("taxa")

## The classes

### Minor component classes

There are a few optional classes used to store information in other classes. These will probably mostly be of interest to developers rather than users.

#### database

Taxonomic data usually comes from a database. A common example is the NCBI Taxonomy Database used to provide taxonomic classifications to sequences deposited in other NCBI databases. The `database` class stores the name of the database and associated information:

    (ncbi <- taxon_database(
      name = "ncbi",
      url = "http://www.ncbi.nlm.nih.gov/taxonomy",
      description = "NCBI Taxonomy Database",
      id_regex = "*"
    ))
    ncbi$name
    ncbi$url

To save on memory, a selection of common databases is provided with the package (`database_list`) and any in this list can be used by name instead of making a new database object (e.g. `"ncbi"` instead of the `ncbi` above).

    database_list

#### rank

Taxa might have defined ranks (e.g. species, family, etc.), ambiguous ranks (e.g. “unranked”, “unknown”), or no rank information at all. The particular selection and format of valid ranks varies with database, so the database can be optionally defined. If no database is defined, any ranks in any order are allowed.

    taxon_rank(name = "species", database = "ncbi")

#### `taxon_name`

The taxon name can be defined in the same way as rank.

    taxon_name("Poa", database = "ncbi")

#### taxon_id

Each database has its set of unique taxon IDs. These IDs are better than using the taxon name directly because they are guaranteed to be unique, whereas there are often duplicates of taxon names (e.g. Orestias elegans is the name of both an orchid and a fish).

    taxon_id(12345, database = "ncbi")

### The “taxon” class

The `taxon` class combines the classes containing the name, rank, and ID for the taxon. There is also a place to define an authority of the taxon.

    (x <- taxon(
      name = taxon_name("Poa annua"),
      rank = taxon_rank("species"),
      id = taxon_id(93036),
      authority = "Linnaeus"
    ))

Instead of the name, rank, and ID classes, simple character vectors can be supplied. These will be converted to objects automatically.

    (x <- taxon(
      name = "Poa annua",
      rank = "species",
      id = 93036,
      authority = "Linnaeus"
    ))

The `taxa` class is just a list of `taxon` classes. It is meant to store an arbitrary list of `taxon` objects.

    grass <- taxon(
      name = taxon_name("Poa annua"),
      rank = taxon_rank("species"),
      id = taxon_id(93036)
    )
    mammalia <- taxon(
      name = taxon_name("Mammalia"),
      rank = taxon_rank("class"),
      id = taxon_id(9681)
    )
    plantae <- taxon(
      name = taxon_name("Plantae"),
      rank = taxon_rank("kingdom"),
      id = taxon_id(33090)
    )

    taxa(grass, mammalia, plantae)

### The “hierarchy” class

Taxonomic classifications are an ordered set of taxa, each at a different rank. The `hierarchy` class stores a list of `taxon` classes like `taxa`, but `hierarchy` is meant to store all of the taxa in a classification in the correct order.

    x <- taxon(
      name = taxon_name("Poaceae"),
      rank = taxon_rank("family"),
      id = taxon_id(4479)
    )

    y <- taxon(
      name = taxon_name("Poa"),
      rank = taxon_rank("genus"),
      id = taxon_id(4544)
    )

    z <- taxon(
      name = taxon_name("Poa annua"),
      rank = taxon_rank("species"),
      id = taxon_id(93036)
    )

    (hier1 <- hierarchy(z, y, x))

Multiple `hierarchy` classes are stored in the `hierarchies` class, similar to how multiple `taxon` are stored in `taxa`.

    a <- taxon(
      name = taxon_name("Felidae"),
      rank = taxon_rank("family"),
      id = taxon_id(9681)
    )
    b <- taxon(
      name = taxon_name("Puma"),
      rank = taxon_rank("genus"),
      id = taxon_id(146712)
    )
    c <- taxon(
      name = taxon_name("Puma concolor"),
      rank = taxon_rank("species"),
      id = taxon_id(9696)
    )
    (hier2 <- hierarchy(c, b, a))

    hierarchies(hier1, hier2)

### The “taxonomy” class

The `taxonomy` class stores unique `taxon` objects in a tree structure. Usually this kind of complex information would be the output of a file parsing function, but the code below shows how to construct a `taxonomy` object from scratch (you would not normally do this).

    # define taxa
    notoryctidae <- taxon(name = "Notoryctidae", rank = "family", id = 4479)
    notoryctes <- taxon(name = "Notoryctes", rank = "genus", id = 4544)
    typhlops <- taxon(name = "typhlops", rank = "species", id = 93036)
    mammalia <- taxon(name = "Mammalia", rank = "class", id = 9681)
    felidae <- taxon(name = "Felidae", rank = "family", id = 9681)
    felis <- taxon(name = "Felis", rank = "genus", id = 9682)
    catus <- taxon(name = "catus", rank = "species", id = 9685)
    panthera <- taxon(name = "Panthera", rank = "genus", id = 146712)
    tigris <- taxon(name = "tigris", rank = "species", id = 9696)
    plantae <- taxon(name = "Plantae", rank = "kingdom", id = 33090)
    solanaceae <- taxon(name = "Solanaceae", rank = "family", id = 4070)
    solanum <- taxon(name = "Solanum", rank = "genus", id = 4107)
    lycopersicum <- taxon(name = "lycopersicum", rank = "species", id = 49274)
    tuberosum <- taxon(name = "tuberosum", rank = "species", id = 4113)
    homo <- taxon(name = "homo", rank = "genus", id = 9605)
    sapiens <- taxon(name = "sapiens", rank = "species", id = 9606)
    hominidae <- taxon(name = "Hominidae", rank = "family", id = 9604)

    # define hierarchies
    tiger <- hierarchy(mammalia, felidae, panthera, tigris)
    cat <- hierarchy(mammalia, felidae, felis, catus)
    human <- hierarchy(mammalia, hominidae, homo, sapiens)
    mole <- hierarchy(mammalia, notoryctidae, notoryctes, typhlops)
    tomato <- hierarchy(plantae, solanaceae, solanum, lycopersicum)
    potato <- hierarchy(plantae, solanaceae, solanum, tuberosum)

    # make taxonomy
    (tax <- taxonomy(tiger, cat, human, tomato, potato))

Unlike the `hierarchies` class, each unique `taxon` object is only represented once in the `taxonomy` object. Each taxon has a corresponding entry in an edge list that encode how it is related to other taxa. This makes `taxonomy` more compact, but harder to manipulate using standard indexing. To make manipulation easier, there are functions like `filter_taxa` and `subtaxa` that will be covered later. In general, the `taxonomy` and `taxmap` objects (covered later) would be instantiated using a parser like `parse_tax_data`. This is covered in detail in the parsing vignette.

#### supertaxa

A “supertaxon” is a taxon of a coarser rank that encompasses the taxon of interest (e.g. “Homo” is a supertaxon of “sapiens”). The `supertaxa` function returns the supertaxa of all or a subset of the taxa in a `taxonomy` object.

    supertaxa(tax)

By default, the taxon IDs for the supertaxa of all taxa are returned in the same order they appear in the edge list. Taxon IDs (character) or edge list indexes (integer) can be supplied to the `subset` option to only return information for some taxa.

    supertaxa(tax, subset = "m")

What is returned can be modified with the `value` option:

    supertaxa(tax, subset = "m", value = "taxon_names")

    supertaxa(tax, subset = "m", value = "taxon_ranks")

You can also subset based on a logical test:

    supertaxa(tax, subset = taxon_ranks == "genus", value = "taxon_ranks")

The `subset` and `value` work the same for most of the following functions as well. See `all_names(tax)` for what can be used with `value` and `subset`. Note how `value` takes a character vector (`"taxon_ranks"`), but `subset` can use the same value (`taxon_ranks`) as a part of an expression. `taxon_ranks` is actually a function that is run automatically when its name is used this way:

    taxon_ranks(tax)

This is an example of Non-standard evaluation (NSE). NSE makes codes easier to read an write. The call to `supertaxa` could also have been written without NSE like so:

    supertaxa(tax, subset = taxon_ranks(tax) == "genus", value = "taxon_ranks")

#### subtaxa

The “subtaxa” of a taxon are all those of a finer rank encompassed by that taxon. For example, sapiens is a subtaxon of Homo. The `subtaxa` function returns all subtaxa for each taxon in a `taxonomy` object.

    subtaxa(tax, value = "taxon_names")

This and the following functions behaves much like `supertaxa`, so we will not go into the same details here.

#### roots

We call taxa that have no supertaxa “roots”. The `roots` function returns these taxa.

    roots(tax, value = "taxon_names")

#### leaves

We call taxa without any subtaxa “leaves”. The `leaves` function returns these taxa.

    leaves(tax, value = "taxon_names")

#### other functions

There are many other functions to interact with `taxonomy` object, such as `stems` and `n_subtaxa`, but these will not be described here for now.

### The “taxmap” class

The `taxmap` class is used to store any number of tables, lists, or vectors associated with taxa. It is basically the same as the `taxonomy` class, but with the following additions:

- A list called `data` that stores arbitrary user data associated with taxa
- A list called `funcs` that stores user defined functions

All the functions described above for the `taxonomy` class can be used with the `taxmap` class.

    info <- data.frame(name = c("tiger", "cat", "mole", "human", "tomato", "potato"),
                       n_legs = c(4, 4, 4, 2, 0, 0),
                       dangerous = c(TRUE, FALSE, FALSE, TRUE, FALSE, FALSE))

    phylopic_ids <- c("e148eabb-f138-43c6-b1e4-5cda2180485a",
                      "12899ba0-9923-4feb-a7f9-758c3c7d5e13",
                      "11b783d5-af1c-4f4e-8ab5-a51470652b47",
                      "9fae30cd-fb59-4a81-a39c-e1826a35f612",
                      "b6400f39-345a-4711-ab4f-92fd4e22cb1a",
                      "63604565-0406-460b-8cb8-1abe954b3f3a")

    foods <- list(c("mammals", "birds"),
                  c("cat food", "mice"),
                  c("insects"),
                  c("Most things, but especially anything rare or expensive"),
                  c("light", "dirt"),
                  c("light", "dirt"))

    reaction <- function(x) {
      ifelse(x$data$info$dangerous,
             paste0("Watch out! That ", x$data$info$name, " might attack!"),
             paste0("No worries; its just a ", x$data$info$name, "."))
    }

    my_taxmap <- taxmap(tiger, cat, mole, human, tomato, potato,
                        data = list(info = info,
                                    phylopic_ids = phylopic_ids,
                                    foods = foods),
                        funcs = list(reaction = reaction))

In most functions that work with taxmap objects, the names of list/vector data sets, table columns, or functions can be used as if they were separate variables on their own (i.e. NSE). In the case of functions, instead of returning the function itself, the results of the functions are returned. To see what variables can be used this way, use `all_names`.

    all_names(my_taxmap)

For example using `my_taxmap$data$info$n_legs` or `n_legs` will have the same effect inside manipulation functions like `filter_taxa` described below. This is similar to how `taxon_ranks` was used in `supertaxa` in a previous section. To get the values of these variables, use `get_data`.

    get_data(my_taxmap)

Note how “taxon_names” and “dangerous” are used below.

#### Filtering

In addition to all of the functions like `subtaxa` that work with `taxonomy`, `taxmap` has a set of functions to manipulate data in a taxonomic context using functions based on dplyr. Like many operations on `taxmap` objects, there are a pair of functions that modify the taxa as well as the associated data, which we call “observations”. The `filter_taxa` and `filter_obs` functions are an example of such a pair that can filter taxa and observations respectively. For example, we can use `filter_taxa` to subset all taxa with a name starting with “t”:

    filter_taxa(my_taxmap, startsWith(taxon_names, "t"))

There can be any number of filters that resolve to TRUE/FALSE vectors, taxon ids, or edge list indexes. For example, below is a combination of a TRUE/FALSE vectors and taxon id filter:

    filter_taxa(my_taxmap, startsWith(taxon_names, "t"), c("b", "r", "o"))

There are many options for `filter_taxa` that make it very flexible. For example, the `supertaxa` option can make all the supertaxa of selected taxa be preserved.

    filter_taxa(my_taxmap, startsWith(taxon_names, "t"), supertaxa = TRUE)

The `filter_obs` function works in a similar way, but subsets observations in `my_taxmap$data`.

    filter_obs(my_taxmap, "info", dangerous == TRUE)

You can choose to filter out taxa whose observations did not pass the filter as well:

    filter_obs(my_taxmap, "info", dangerous == TRUE, drop_taxa = TRUE)

Note how both the taxonomy and the associated data sets were filtered. The `drop_obs` option can be used to specify which non-target (i.e. not `"info"`) data sets are filtered when taxa are removed.

#### Sampling

The functions `sample_n_obs` and `sample_n_taxa` are similar to `filter_obs` and `filter_taxa`, except taxa/observations are chosen randomly. All of the options of the “filter_” functions are available to the “sample_” functions

    set.seed(1)
    sample_n_taxa(my_taxmap, 3) # "3" here is a taxon index in the edge list
    set.seed(1)
    sample_n_taxa(my_taxmap, 3, supertaxa = TRUE)

#### Adding columns

Adding columns to tabular data sets is done using `mutate_obs`.

    mutate_obs(my_taxmap, "info",
               new_col = "Im new",
               newer_col = paste0(new_col, "er!"))

Note how you can use newly created columns in the same call.

#### Subsetting columns

Subsetting columns in tabular data sets is done using `select_obs`.

    # Selecting a column by name
    select_obs(my_taxmap, "info", dangerous)

    # Selecting a column by index
    select_obs(my_taxmap, "info", 3)

    # Selecting a column by regular expressions (i.e. TRUE/FALSE)
    select_obs(my_taxmap, "info", matches("^dange"))

#### Sorting

Sorting the edge list and observations is done using `arrage_taxa` and `arrange_obs`.

    arrange_taxa(my_taxmap, taxon_names)
    arrange_obs(my_taxmap, "info", name)

#### Parsing data

The `taxmap` class has the ability to contain and manipulate very complex data. However, this can make it difficult to parse the data into a `taxmap` object. For this reason, there are three functions to help creating `taxmap` objects from nearly any kind of data that a taxonomy can be associated with or derived from. The figure below shows simplified versions of how to create `taxmap` objects from different types of data in different formats.

The `parse_tax_data` and `lookup_tax_data` have, in addition to the functionality above, the ability to include additional data sets that are somehow associated with the source data sets (e.g. share a common identifier). Elements in these data sets will be assigned the taxa defined in the source data, so functions like `filter_taxa` and `filter_obs` will work on all of the data set at once. See the parsing vignette for more information.

## Parsing Hierarchy and hierarchies objects

A set of functions are available for parsing objects of class `Hierarchy` and `hierarchies`. These functions are being ported from the CRAN package `binomen`.

The functions below are “taxonomically aware” so that you can use for example `>` and `<` operators to filter your taxonomic names data.

### pick

`pick()` - Pick out specific taxa, while others are dropped

    ex_hierarchy1
    # specific ranks by rank name
    pick(ex_hierarchy1, ranks("family"))
    # two elements by taxonomic name
    pick(ex_hierarchy1, nms("Poaceae", "Poa"))
    # two elements by taxonomic identifier
    pick(ex_hierarchy1, ids(4479, 4544))
    # combine types
    pick(ex_hierarchy1, ranks("family"), ids(4544))

### pop

`pop()` - Pop out taxa, that is, drop them

    ex_hierarchy1
    # specific ranks by rank name
    pop(ex_hierarchy1, ranks("family"))
    # two elements by taxonomic name
    pop(ex_hierarchy1, nms("Poaceae", "Poa"))
    # two elements by taxonomic identifier
    pop(ex_hierarchy1, ids(4479, 4544))
    # combine types
    pop(ex_hierarchy1, ranks("family"), ids(4544))

### span

`span()` - Select a range of taxa, either by two names, or relational operators

    ex_hierarchy1
    # keep all taxa between family and genus
    # - by rank name, taxonomic name or ID
    span(ex_hierarchy1, nms("Poaceae", "Poa"))

    # keep all taxa greater than genus
    span(ex_hierarchy1, ranks("> genus"))

    # keep all taxa greater than or equal to genus
    span(ex_hierarchy1, ranks(">= genus"))

    # keep all taxa less than Felidae
    span(ex_hierarchy2, nms("< Felidae"))

    ## Multiple operator statements - useful with larger classifications
    ex_hierarchy3
    span(ex_hierarchy3, ranks("> genus"), ranks("< phylum"))

## For more information

This vignette is meant to be just an outline of what `taxa` can do. In the future, we plan to release additional, in-depth vignettes for specific topics. More information for specific functions and examples can be found on their man pages by typing the name of the function prefixed by a `?` in an R session. For example, `?filter_taxa` will pull up the help page for `filter_taxa`.