tree.py

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High-level description

The Tree class represents a phylogenetic tree and provides methods for manipulating, analyzing, and visualizing it. It supports constructing trees from Newick files, generating trees by simulation, and performing various operations like annotating nodes with features, calculating tree statistics, and inferring fitness.

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Code Structure

The Tree class encapsulates an ete3.Tree object and extends its functionality with custom methods. It utilizes external libraries like ete3 for tree manipulation, Bio.Phylo for interfacing with Biopython, and other modules for specific tasks like site frequency spectrum analysis and fitness inference.

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References

This code references the following external libraries and modules:

• ete3: Used for phylogenetic tree manipulation and visualization.
• Bio.Phylo: Used for interfacing with Biopython’s phylogenetic tree representation.
• .resources.betatree.src.betatree: Used for simulating trees using the beta-tree model.
• .resources.FitnessInference.prediction_src.node_ranking: Used for inferring fitness metrics of nodes.
• jungle.sfs.SFS: Used for calculating and analyzing site frequency spectra.

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Symbols

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Tree

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Description

This class represents a phylogenetic tree and provides methods for its manipulation, analysis, and visualization.

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Inputs

Name	Type	Description
T	ete3.Tree	An ete3.Tree object representing the phylogenetic tree.
name	str	The name of the tree.
params	dict	A dictionary of parameters used to generate or analyze the tree.

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Outputs

This class does not have a return value. It is used to create and manipulate Tree objects.

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Internal Logic

The Tree class stores the tree structure in an ete3.Tree object and provides methods for:

• Loading and saving trees from/to files.
• Generating trees by simulation.
• Annotating nodes with various features like depth, number of descendants, imbalance, etc.
• Calculating tree statistics like total branch length, site frequency spectrum, and various diversity indices.
• Inferring fitness of nodes using external packages.
• Visualizing the tree with node coloring and rendering.

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Side Effects

Some methods of the Tree class modify the internal state of the ete3.Tree object, such as adding new attributes to nodes or changing branch lengths.

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Performance Considerations

The performance of some methods, especially those involving tree traversal or complex calculations, may vary depending on the size and complexity of the tree.

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from_newick

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Description

Constructs a Tree object from a Newick file.

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Inputs

Name	Type	Description
filename	str	The path to the Newick file.
name	str	The name of the tree (optional).
params	dict	A dictionary of parameters (optional).

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Outputs

Name	Type	Description
tree	Tree	A Tree object representing the tree from the Newick file.

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Internal Logic

• Reads the Newick file using ete3.Tree.
• Ladderizes the tree for consistent visualization.
• Assigns names to internal nodes if not already present.

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from_pickle

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Description

Loads a Tree object from a pickle file.

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Inputs

Name	Type	Description
filename	str	The path to the pickle file.
gzip	bool	Whether the file is gzipped (optional, inferred from filename if not provided).

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Outputs

Name	Type	Description
tree	Tree	A Tree object loaded from the pickle file.

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Internal Logic

• Opens the pickle file, handling gzip compression if necessary.
• Loads the Tree object using pickle.load.

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generate

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Description

Generates a random Tree object using the beta-tree model.

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Inputs

Name	Type	Description
params	dict	A dictionary of parameters for tree generation, including ‘n_leaves’ (number of leaves) and ‘alpha’ (shape parameter of the beta distribution).
name	str	The name of the tree (optional).

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Outputs

Name	Type	Description
tree	Tree	A randomly generated Tree object.

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Internal Logic

• Uses the betatree module to simulate a tree with the given parameters.
• Converts the simulated tree to an ete3.Tree object.
• Ladderizes the tree and assigns names to internal nodes.

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to_newick

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Description

Writes the Tree object to a Newick file.

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Inputs

Name	Type	Description
outfile	str	The path to the output Newick file.
**kwargs	keyword arguments	Additional arguments passed to ete3.Tree.write.

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Outputs

This method does not return any value. It writes the tree to a file.

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Internal Logic

• Uses the ete3.Tree.write method to write the tree to the specified file in Newick format.

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annotate_standard_node_features

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Description

Annotates each node in the tree with standard features like depth, number of children, and number of descendants.

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Inputs

This method does not take any inputs.

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Outputs

This method does not return any value. It modifies the tree in place.

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Internal Logic

• Traverses the tree in postorder.
• For each node, calculates and sets the following attributes:
  • depth: Distance from the root.
  • num_children: Number of direct children.
  • num_descendants: Total number of descendants, including the node itself.
  • num_leaf_descendants: Total number of leaf nodes that descend from this node.
• Sets the is_depth_annotated flag to True.
• Calculates and sets the depth_normalized attribute for each node, normalized by the maximum depth.

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node_features

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Description

Returns a Pandas DataFrame containing selected features of all nodes in the tree.

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Inputs

Name	Type	Description
subset	list	A list of feature names to include in the DataFrame (optional, defaults to all available features).

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Outputs

Name	Type	Description
features	pandas.DataFrame	A DataFrame with rows representing nodes and columns representing selected features.

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Internal Logic

• Determines the set of features to include in the DataFrame.
• Iterates through each feature and each node, retrieving the feature value (or None if not available) and storing it in the DataFrame.
• Adds an ‘is_leaf’ column indicating whether each node is a leaf.

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annotate_imbalance

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Description

Calculates and annotates each node with its imbalance, defined as the ratio of the maximum number of descendants among its children to the total number of descendants.

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Inputs

This method does not take any inputs.

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Outputs

This method does not return any value. It modifies the tree in place.

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Internal Logic

• Traverses the tree.
• For each non-leaf node:
  • Retrieves the number of descendants for each child node.
  • Calculates the imbalance as the maximum number of descendants divided by the total number of descendants.
  • Sets the ‘imbalance’ attribute of the node.

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annotate_colless

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Description

Calculates and annotates each node with its Colless index, a measure of tree balance.

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Inputs

This method does not take any inputs.

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Outputs

This method does not return any value. It modifies the tree in place.

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Internal Logic

• Traverses the tree in postorder.
• For each node:
  • If it’s a leaf node, sets the ‘colless’ attribute to 0.
  • If it’s an internal node:
    • Calculates the absolute difference in the number of descendants between its two children.
    • Recursively calculates the Colless index for each child.
    • Calculates the Colless index for the current node by summing the difference in descendants and the Colless indices of its children.
  • Sets the ‘difference_num_descendants’, ‘colless’, and ‘log10p_colless’ attributes of the node.
• Sets the ‘colless’ and ‘log10p_colless’ attributes of the Tree object itself.

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max_depth

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Description

Returns the maximum depth of the tree.

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Inputs

This method does not take any inputs.

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Outputs

Name	Type	Description
max_depth	int	The maximum depth of the tree.

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Internal Logic

• Checks if the is_depth_annotated flag is True. If not, raises an error.
• Retrieves the ‘depth’ attribute of all nodes and returns the maximum value.

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total_branch_length

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Description

Calculates and returns the total branch length of the tree.

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Inputs

This method does not take any inputs.

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Outputs

Name	Type	Description
total_branch_length	float	The total branch length of the tree.

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Internal Logic

• Sums the ‘dist’ attribute (branch length) of all nodes in the tree.

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rescale

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Description

Rescales the tree so that its total branch length equals a given value.

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Inputs

Name	Type	Description
total_branch_length	float	The desired total branch length after rescaling.

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Outputs

This method does not return any value. It modifies the tree in place.

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Internal Logic

• Calculates the current total branch length.
• Calculates the scaling factor as the desired length divided by the current length.
• Multiplies the ‘dist’ attribute (branch length) of each node by the scaling factor.

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resolve_polytomy

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Description

Resolves any polytomies (nodes with more than two children) in the tree by creating an arbitrary dichotomous structure.

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Inputs

This method does not take any inputs.

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Outputs

This method does not return any value. It modifies the tree in place.

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Internal Logic

• Uses the ete3.Tree.resolve_polytomy method to resolve polytomies.
• Ladderizes the tree to maintain a consistent visualization.

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site_frequency_spectrum

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Description

Calculates and returns the site frequency spectrum (SFS) of the tree.

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Inputs

This method does not take any inputs.

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Outputs

Name	Type	Description
sfs	SFS	An SFS object representing the site frequency spectrum of the tree.

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Internal Logic

• If the _site_frequency_spectrum attribute is not already calculated:
  • Calculates the SFS using the SFS.from_tree method.
  • Stores the result in the _site_frequency_spectrum attribute.
• Returns the _site_frequency_spectrum attribute.

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bin_site_frequency_spectrum

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Description

Bins the site frequency spectrum (SFS) of the tree using specified bins.

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Inputs

Name	Type	Description
bins	array-like	An array-like object defining the bin edges.
*args	tuple	Additional positional arguments passed to the SFS.bin method.
**kwargs	dict	Additional keyword arguments passed to the SFS.bin method.

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Outputs

Name	Type	Description
binned_sfs	array-like	An array-like object containing the binned and normalized SFS values.

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Internal Logic

• Calls the SFS.bin method on the tree’s SFS with the provided arguments.
• Returns the binned_normalized_cut attribute of the SFS object, which represents the binned and normalized SFS values.

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fay_and_wus_H

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Description

Calculates and returns Fay and Wu’s H statistic, a measure of genetic diversity, from the tree’s SFS.

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Inputs

This method does not take any inputs.

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Outputs

Name	Type	Description
H	float	Fay and Wu’s H statistic.

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Internal Logic

• If the _fay_and_wus_H attribute is not already calculated:
  • Calculates H using the SFS.fay_and_wus_H method.
  • Stores the result in the _fay_and_wus_H attribute.
• Returns the _fay_and_wus_H attribute.

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zengs_E

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Description

Calculates and returns Zeng’s E statistic, a measure of genetic diversity, from the tree’s SFS.

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Inputs

This method does not take any inputs.

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Outputs

Name	Type	Description