Importing and Exporting HiCExplorer data

Exporting HiCExplorer output to Bioconductor

It’s possible to export Hi-C Matrices produced by HiCExplorer to bioconductor in R, which allows us to use existing bioconductor infrastructure for differential Hi-C analysis. The tool hicExport allows us to write Hi-C matrices in a format that can eaisily be imported in bioconductor as GInteractions object. Below is an example.

## Assuming HiCExplorer is installed in ~/programs
hicExport --inFile ~/programs/HiCExplorer/test/test_data/Li_et_al_2015.h5 \
-o GInteration_example --outputFormat GInteractions

The output file is in tsv format. It looks like this :

V1	V2	V3	V4	V5	V6	V7
X	19537	20701	X	19537	20701	1054.47483
X	19537	20701	X	20701	22321	375.86990
X	19537	20701	X	22321	24083	222.53900
X	19537	20701	X	24083	25983	114.26340
X	19537	20701	X	25983	27619	95.87463

This file can now be loaded into R as a GInteractions object, as shown below :

## INSIDE R
library(GenomicRanges)
library(InteractionSet)

hic <- read.delim("GInteraction_example.tsv", header = FALSE)

# Converting data.frame to GInteraction
convertToGI <- function(df){
            row.regions <- GRanges(df$V1, IRanges(df$V2,df$V3))# interaction start
            col.regions <- GRanges(df$V4, IRanges(df$V5,df$V6))# interaction end
            gi <- GInteractions(row.regions, col.regions)
            gi$norm.freq <- df$V7 # Interaction frequencies
            return(gi)
}
                        }
hic.gi <- convertToGI(hic)

Multiple files can be loaded, and converted to an InteractionSet object. If you have prepared matrices using binning, the intervals in the matrices must be the same. Therefore it’s easy to merge these matrices together in an InteractionSet object. In case some bins don’t match, we can merge the GInteraction objects based on matching bins, as follows.

# assuming hic.gi is a list of two GInteration objects hic.gi1 and hic.gi2
# hic.gi <- list(hic.gi1, hic.gi2)

# Get common regions between the two objects
combined <- unique(c(hic.gi$hic.gi1, hic.gi$hic.gi2))

# replace original regions with the common regions
replaceRegions(hic.gi$hic.gi1) <- regions(combined)
replaceRegions(hic.gi$hic.gi2) <- regions(combined)

# Get the matching indexes between the two objects
matched <- lapply(hic.gi, function(x) {
            match(x, combined)
            })

# Create a count matrix (for interaction frequencies)
counts <- matrix(0, ncol = 2, nrow=length(combined)) # counts for unmatched bins set to zero

# fill in the counts for matched bins
counts[matched$hic.gi1,1] <- hic.gi$hic.gi1$norm.freq
counts[matched$hic.gi2,2] <- hic.gi$hic.gi2$norm.freq

# Finally, create the InteractionSet object
iset <- InteractionSet(counts, combined)

InteractionSet objects can be used for packages like diffHic, for differential Hi-C analysis.

• For more information on working with GInteraction and InteractionSet objects in bioconductor check out this vignette.