# Other Data Formats And Customizations

#### Thomas Charlon

#### 2024-09-09

# Other Data Formats And Customizations

SNPLinkage is modular enough to use directly dataframes of correlation matrices and chromosomic positions specified by the user, e.g. for visualizing RNASeq data. The user can compute a correlation matrix or any kind of pair-wise similarity matrix independently and then use SNPLinkage to build and arrange easily customizable ggplot2 objects.

## Building the correlation matrix plot

The user can specify the correlations he wants to visualize as a dataframe to the `ggplot_ld` function. The column names must follow the following pattern: `SNP_A` and `SNP_B` for the two variables in relation, and `R2` for the correlation value.

      library(snplinkage)
    #> Loading required package: GWASTools
    #> Loading required package: Biobase
    #> Loading required package: BiocGenerics
    #>
    #> Attaching package: 'BiocGenerics'
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    #>     duplicated, eval, evalq, get, grep, grepl, intersect, is.unsorted,
    #>     lapply, mapply, match, mget, order, paste, pmax, pmax.int, pmin,
    #>     pmin.int, rank, rbind, rownames, sapply, setdiff, table, tapply,
    #>     union, unique, unsplit, which.max, which.min
    #> Welcome to Bioconductor
    #>
    #>     Vignettes contain introductory material; view with
    #>     'browseVignettes()'. To cite Bioconductor, see
    #>     'citation("Biobase")', and for packages 'citation("pkgname")'.

      # example rnaseq data matrix, 20 variables of 20 patients
      m_rna = matrix(runif(20 ^ 2), nrow = 20)

      # pair-wise correlation matrix
      m_ld = cor(m_rna) ^ 2

      # keep only upper triangle and reshape to data frame
      m_ld[lower.tri(m_ld, diag = TRUE)] = NA
      df_ld = reshape2::melt(m_ld) |> na.omit()

      # rename for SNPLinkage
      names(df_ld) = c('SNP_A', 'SNP_B', 'R2')

      # visualize with ggplot_ld
      gg_ld = ggplot_ld(df_ld)
      gg_ld

## Adding chromosomic positions

Similarly, the user can specify a dataframe to the `ggplot_snp_pos` function. The dataframe is assumed to be in the same order as the correlation dataframe, and the column name `position` is required.

      # let's imagine the 20 variables came from 3 physically close regions
      positions = c(runif(7, 31e6, 31.5e6), runif(6, 32e6, 32.5e6),
                    runif(7, 33e6, 33.5e6)) |> sort()

      # build the dataframe
      df_snp_pos = data.frame(position = positions)

      # minimal call
      gg_snp_pos = ggplot_snp_pos(df_snp_pos)

Optionally, one can specify the `labels_colname` parameter to give the name of a column that will have the labels to display.

      df_snp_pos$label = c(rep('HLA-A', 7), rep('HLA-B', 6), rep('HLA-C', 7))
      gg_snp_pos = ggplot_snp_pos(df_snp_pos, labels_colname = 'label')

## Arranging the plots together

We then arrange the plots with the `gtable_ld_grobs` function. One needs to specify in the `labels_colname` parameter if the chromosomic positions plot was built with labels or not. The `title` parameter is also required.

      l_ggs = list(snp_pos = gg_snp_pos, ld = gg_ld)
      gt_ld = gtable_ld_grobs(l_ggs, labels_colname = TRUE,
                              title = 'RNASeq correlations')
      grid::grid.draw(gt_ld)

## Adding associations values

Finally we add the variables’ associations to our outcome of interest. The `ggplot_associations` uses as input a dataframe and accepts a parameter `pvalue_colname` to specify which column holds the association values, by default ‘pvalues’. It also requires a `labels_colname` parameter to specify the column holding the labels, and a column named `chromosome`. The `linked_area` parameter will affect how the associations are plotted and it is recommended to be used in combination with the `diamonds` parameter of `ggplot_ld` (i.e. TRUE for small number of variables, approximately less than 40).

Additionally, the `n_labels` parameter controls the number of highest association labels displayed (be default 10, the behavior can be disabled by setting `labels_colname` to NULL), and the `nudge` parameter will affect how the labels are displayed (passed to `geom_label_repel` function of ‘ggrepel’ package).

      # let's imagine the middle region, HLA-B, is more associated with the outcome
      pvalues = c(runif(7, 1e-3, 1e-2), runif(6, 1e-8, 1e-6), runif(7, 1e-3, 1e-2))
      log10_pvals = -log10(pvalues)

      # we can reuse the df_snp_pos object
      df_snp_pos$pvalues = log10_pvals

      # add the chromosome column
      df_snp_pos$chromosome = 6

      gg_assocs = ggplot_associations(df_snp_pos, labels_colname = 'label',
                                      linked_area = TRUE, nudge = c(0, 0.5),
                                      n_labels = 12)

We then arrange the plots with the `gtable_ld_grobs` function as previously. We need to call the `ggplot_snp_pos` function with the `upper_subset` parameter set to TRUE for it to connect to the upper graph.

      gg_pos_biplot = ggplot_snp_pos(df_snp_pos, labels_colname = 'label',
                                     upper_subset = TRUE)

      # let's also say the middle region HLA-B is particularly correlated
      df_ld$R2[df_ld$SNP_A %in% 8:13 & df_ld$SNP_B %in% 8:13] = runif(15, 0.7, 0.9)
      gg_ld = ggplot_ld(df_ld)

      l_ggs = list(pos = gg_pos_biplot, ld = gg_ld, pval = gg_assocs)
      gt_ld = gtable_ld_associations_combine(l_ggs, diamonds = TRUE)

We can extract a title and remove the horizontal axis text as follows.

      library(ggplot2)
      gg_assocs <- gg_assocs + theme(axis.text.x = element_blank())
      title <- gg_assocs$labels$x %>% gsub(' (Mbp)', '', ., fixed = TRUE) %>%
        paste('-', nrow(df_snp_pos), 'SNPs')
      gg_assocs <- gg_assocs + labs(title = title, x = NULL)

      l_ggs$pval = gg_assocs
      gt_ld = gtable_ld_associations_combine(l_ggs, diamonds = TRUE)
      grid::grid.draw(gt_ld)

## Customizing the ggplots

Let’s say we want to change the color of the associations area. We first need to identify which layer it corresponds to:

      gg_assocs$layers
    #> [[1]]
    #> geom_area: na.rm = FALSE, orientation = NA, outline.type = upper
    #> stat_align: na.rm = FALSE, orientation = NA
    #> position_stack
    #>
    #> [[2]]
    #> mapping: xend = ~x
    #> geom_segment: arrow = NULL, arrow.fill = NULL, lineend = butt, linejoin = round, na.rm = FALSE
    #> stat_identity: na.rm = FALSE
    #> position_identity
    #>
    #> [[3]]
    #> geom_label_repel: parse = FALSE, box.padding = 0.25, label.padding = 0.1, point.padding = 1e-06, label.r = 0.15, label.size = 0.1, min.segment.length = 0.5, arrow = NULL, na.rm = TRUE, force = 1, force_pull = 1, max.time = 0.5, max.iter = 10000, max.overlaps = 10, nudge_x = 0, nudge_y = 0.5, xlim = c(NA, NA), ylim = c(NA, NA), direction = both, seed = NA, verbose = FALSE
    #> stat_identity: na.rm = TRUE
    #> position_nudge_repel
    #>
    #> [[4]]
    #> geom_point: na.rm = FALSE
    #> stat_identity: na.rm = FALSE
    #> position_identity

Then we can change the color with:

      gg_assocs$layers[[1]]$aes_params$fill = "#0147ab"

And rebuild our object.

      l_ggs$pval = gg_assocs
      gt_ld = gtable_ld_associations_combine(l_ggs, diamonds = TRUE)

To change the lines and labels colors, parameters in the functions are available. You can either specify a single value or a vector of same length as your number of features.

      gg_pos_biplot = ggplot_snp_pos(df_snp_pos, labels_colname = 'label',
                                     upper_subset = TRUE, colors = '#101d6b')

      gg_assocs = ggplot_associations(df_snp_pos, labels_colname = 'label',
                                      linked_area = TRUE, nudge = c(0, 0.5),
                                      n_labels = 12, colors = '#101d6b')

      # extract title
      gg_assocs <- gg_assocs + theme(axis.text.x = element_blank())
      title <- gg_assocs$labels$x %>% gsub(' (Mbp)', '', ., fixed = TRUE) %>%
        paste('-', nrow(df_snp_pos), 'SNPs')
      gg_assocs <- gg_assocs + labs(title = title, x = NULL)

      # replace area color
      gg_assocs$layers[[1]]$aes_params$fill = "#0147ab"

      # rebuild
      l_ggs = list(pos = gg_pos_biplot, ld = gg_ld, pval = gg_assocs)
      gt_ld = gtable_ld_associations_combine(l_ggs, diamonds = TRUE)
      grid::grid.draw(gt_ld)

## Example on Crohn dataset from gap package

In this dataset from the ‘gap’ package (Zhao, Kurt Hornik, and Ripley 2015), 206 SNPs from chromosome 5 (5q31) were measured from 129 Crohn’s disease patients and their 2 parents, totalling 387 samples.

      data('crohn')
      m_hla = crohn[, -(1:6)]
      m_ld = cor(m_hla) ^ 2

      # keep only upper triangle and reshape to data frame
      m_ld[lower.tri(m_ld, diag = TRUE)] = NA
      df_ld = reshape2::melt(m_ld) |> na.omit()

      # rename for SNPLinkage
      names(df_ld) = c('SNP_A', 'SNP_B', 'R2')

      # visualize with ggplot_ld
      gg_ld = ggplot_ld(df_ld)

Compute p-values

      mlog10_pvals = chisq_pvalues(m_hla, crohn[, 'crohn'])
      df_pos = data.frame(probe_id = colnames(m_hla), pvalues = mlog10_pvals,
                          chromosome = 5)

      # if we don't have positions we can use byindex = TRUE
      gg_assocs = ggplot_associations(df_pos, byindex = TRUE, nudge = c(0, 0.5))

Arrange with ‘cowplot’

      cowplot::plot_grid(gg_assocs, gg_ld, nrow = 2)

Focus on most associated

      df_top_assocs = subset(df_pos, pvalues > quantile(pvalues, 0.9))
      gg_assocs = ggplot_associations(df_top_assocs, linked_area = TRUE,
                                      nudge = c(0, 0.5))

      df_ld = subset(df_ld, SNP_A %in% df_top_assocs$probe_id &
                            SNP_B %in% df_top_assocs$probe_id)

      gg_ld = ggplot_ld(df_ld)

      cowplot::plot_grid(gg_assocs, gg_ld, nrow = 2)

## References

Zhao, Jing Hua, colleagues with inputs from Kurt Hornik, and Brian Ripley. 2015. : Genetic Analysis Package. https://CRAN.R-project.org/package=gap.

## Session information

      sessionInfo()
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    #> Running under: Ubuntu 22.04.4 LTS
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    #> [1] ggplot2_3.5.1       snplinkage_1.2.0    GWASTools_1.50.0
    #> [4] Biobase_2.64.0      BiocGenerics_0.50.0
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