Tabular data analysis

Leo Lahti

Recap of Day 1

• Data: SummarizedExperiment: rowData, colData, assays
• Methods: subsetting, transformations

Day 1: Basic data wrangling

• reproducible data science workflow
• data import
• data containers
• data manipulation (subsetting, transformations)

Today’s learning goals

Expanding multi-assay analyses:
TreeSummarizedExperiment

• augmenting the data (add diversities)
• data agglomeration & alternative experiments
• tree information: rowTree, colTree

Today’s program

Morning: data wrangling

Afternoon: data visualizations

Data enrichment

Visualizing colData

Task: visualize the abundance of a specific microbial Species against the measurement Site

Alpha diversity task

Use the available tools to assess and visualize alpha diversity, and augment colData

• Exercises 17.5.1-17.5.2
• Add Shannon diversity in colData
• Visualize diversity differences between sample groups

Alpha diversity & aging

Healthy & normal obese subjects.

Alpha diversity and diet

Alpha diversity

• How many types?

• Distribution of types?

• Dominance of types?

Alpha diversity

• How many types?

• Distribution of types?

• Dominance of types?

Alpha diversity indices

Richness

• number of types

• Eetimates of true richness based on finite sample sizes (Howard Sanders 1968); see e.g. Chao1

Evenness

• distribution of sizes (even or uneven?)

Diversity

• Combining richness & evenness

Dominance

Finite sampling

https://github.com/mblstamps/stamps2019/blob/master/STAMPS2019_overview_Pop.pdf

High-quality reference genomes are required for functional characterization and taxonomic assignment of the human gut microbiota.

Unified Human Gastrointestinal Genome (UHGG):

• 4,644 gut prokaryotes (>70% lack cultured representatives)

• 204,938 nonredundant genomes

• Encode >170 million protein sequences, collated into Unified Human Gastrointestinal Protein (UHGP) catalog.

UHGP more than doubles the number of gut proteins in comparison to those present in the Integrated Gene Catalog.

• 40% of the UHGP lack functional annotations

• Intraspecies genomic variation analyses revealed a large reservoir of accessory genes and single-nucleotide variants, many of which are specific to individual human populations.

The UHGG and UHGP collections enable studies linking genotypes to phenotypes in the human gut microbiome.

Estimating species content

Copyright © Claudia Zirion, Diego Garfias, Vanessa Arellano, Aaron Jaime, Abel Lovaco, Daniel Díaz, Abraham Avelar, Nelly Sélem https://carpentries-incubator.github.io/metagenomics-workshop/)

Common alpha diversity indices

Phylogenetically neutral diversities:

• Richness (observed, Chao1, ACE)
• Evenness (Pielou’s evenness)
• Diversity (inverse Simpson, Shannon)

Phylogeny-aware diversities:

• Faith diversity index

Phylogenetic diversity indices

Inverse Simpson

How likely it is to pick two members of the same species at random?

Inverse Simpson

Beware the variants:

• Simpson (\(\lambda\))

• reciprocal Simpson (\(1-\lambda\))

• inverse Simpson (\(\frac{1}{\lambda}\))

Shannon diversity

Shannon Index:

True Richness:

True diversity, or the effective number of types, refers to the number of equally abundant types needed for the average proportional abundance of the types to equal what is observed in the dataset of interest.

Evenness

H / ln(S)

• H: Shannon diversity
• S: Species richness

Hill’s Diversity as a unifying concept

\[\begin{equation} ^qD = (\sum_i^R p_i^q )^\frac{1}{1-q} \end{equation}\]

Hill’s alpha diversities

R: richness (number of distinct types)

pi: proportion of type I

Order of diversity:

• q = 0 : Species Richness
• q = 1 : Shannon diversity
• q = 2 : (Inverse) Simpson diversity
• q ≠ 1 : Renyi entropy

Hill’s Diversity as a unifying concept

Hill’s alpha diversities

• Richness
• inverse Simpson
• Shannon

Data wrangling

Basic data operations

• Transform

• Subset

• Merge

• Aggregate

• Split

Subsetting

Load example data set:

library(mia)
data(GlobalPatterns)
tse <- GlobalPatterns

Check dimension:

dim(tse)

[1] 19216    26

Check dimension for a subset:

dim(tse[1:10, 1:3])

[1] 10  3

Transformations

• Presence/absence
• Compositional (percentages)
• \(Log_{10}\)
• CLR and other Aitchison transformations
• Phylogenetic transformations (e.g. philr)
• Custom transformations

Transformations

Task: Alternative assays

• visualize transformed data; histograms, boxplots
• compare different transformations (scatterplot?)

Agglomeration

• taxonomic units
• TreeSE objects

Agglomeration

Agglomerate microbiota data to higher taxonomic levels:

• chapter 6.3
• agglomerateByRank
• compare diversity or prevalent features between levels

Alternative experiments

Alternative assays vs. alternative experiments?

• Store agglomerated data: altExp
• Do all levels at once: splitByRanks

Splits

Splitting by:

• taxonomic units
• sample or feature groups

Taxonomic ranks & altExp

The alternative experiments (altExp) mechanism allows us to include multiple abundance tables at different taxonomic levels.

Option	Rows (features)	Cols (samples)	Recommendation
assays	match	match	Data transformations
altExp	free	match	Alternative experiments
MultiAssay	free	free (mapping)	Multi-omic experiments

Alternative experiments and assays?

• Pick clr assay from Genus-level data table?
• Compare Shannon diversity from Genus and Species levels?

TreeSummarizedExperiment

Huang et al. F1000, 2021

Visualization

Ordination

• Visualize example data with PCoA using Bray-Curtis dissimilarity
• Visualize example data with PCA using Aitchison distance (CLR + Euclid)

Heatmaps

• Visualize abundance variation for selected taxa on a heatmap

Trees

• Visualize phylogenetic tree using the examples