mva {lipidr} | R Documentation

## Perform multivariate analyses to investigate sample clustering

### Description

`mva` performs multivariate analysis using several possible methods. The available methods are PCA, PCoA, OPLS and OPLS-DA. The OPLS method requires a numeric y-variable, whilst OPLS-DA requires two groups for comparison. By default, for OPLS and OPLS-DA the number of predictive and orthogonal components are set to 1. Blank samples are automatically detected (using TIC) and excluded. Missing data are imputed using average lipid intensity across all samples.

### Usage

    mva(data, measure = "Area", method = c("PCA", "PCoA", "OPLS",
      "OPLS-DA"), group_col = NULL, groups = NULL, ...)

    plot_mva(mvaresults, components = c(1, 2), color_by = NULL,
      ellipse = TRUE, hotelling = TRUE)

    plot_mva_loadings(mvaresults, components = c(1, 2), color_by = NULL,
      top.n = nrow(mvaresults$loadings))

    top_lipids(mvaresults, top.n = 10)

### Arguments

`data` | LipidomicsExperiment object.
`measure` | Which measure to use as intensity, usually Area (default). The measure should be already summarized and normalized.
`method` | Either PCA, PCoA, OPLS or OPLS-DA. Default is `PCA`.
`group_col` | Sample annotation to use as grouping column. If not provided, samples are treated independently.
`groups` | A numeric grouping (OPLS) or two groups to be used for supervised analysis (OPLS-DA), ignored in other methods.
`...` | Extra arguments to be passed to `opls()` for OPLS-DA, ignored in other methods.
`mvaresults` | Results obtained from `mva()`.
`components` | Which components to plot. Ignored for PCoA, OPLS and OPLS-DA results. Default is first 2 components.
`color_by` | Sample annotation (or lipid annotation in case of `plot_mva_loadings`) to use as color. Defaults to individual samples / lipids
`ellipse` | Whether to plot ellipses around groups
`hotelling` | Whether to plot Hotelling T2.
`top.n` | Number of top ranked features to highlight in the plot. If omitted, returns top 10 lipids.

### Value

Multivariate analysis results in `mvaresults` object. The object contains the following:

- scores Sample scores

- loadings Feature or component loadings (not for PCoA)

- method Multivariate method that was used

- row_data Lipid molecule annotations

- col_data Sample annotations

- original_object Original output object as returned by corresponding analysis methods

`plot_mva` returns a ggplot of the sample scores.

`plot_mva_loadings` returns a ggplot of the loadings.

`top_lipids` returns s dataframe of `top.n` lipids with their annotations.

### Functions

- `plot_mva`: plots a multivariate scatterplot of sample scores to investigate sample clustering.

- `plot_mva_loadings`: Plot a multivariate scatterplot of feature loadings to investigate feature importance.

- `top_lipids`: extracts top lipids from OPLS-DA results

### Examples

    data(data_normalized)

    # PCA
    mvaresults <- mva(data_normalized, measure = "Area", method = "PCA")
    plot_mva(mvaresults, color_by = "group")
    # NOT RUN
    # plot_mva(mvaresults, color_by = "Diet", components = c(2, 3))

    # PCoA
    mvaresults <- mva(data_normalized, measure = "Area", method = "PCoA")
    # NOT RUN
    # plot_mva(mvaresults, color_by = "group")

    # OPLS-DA
    mvaresults <- mva(
      data_normalized,
      method = "OPLS-DA", group_col = "Diet", groups = c("HighFat", "Normal")
    )
    plot_mva(mvaresults, color_by = "group")
    plot_mva_loadings(mvaresults, color_by = "Class", top.n = 10)
    top_lipids(mvaresults, top.n = 10)

[Package lipidr version 2.0.0 Index]