savePairs {diffHic} | R Documentation

## Save Hi-C read pairs

### Description

Save a dataframe of read pairs into a directory structure for rapid chromosomal access.

### Usage

    savePairs(x, file, param)

### Arguments

`x` | A dataframe with integer fields `anchor1.id` and `anchor2.id`. Each row corresponds to a single read pair.
`file` | A character string specifying the path for the output index file.
`param` | A `pairParam` object containing read extraction parameters. In particular, `param$fragments` should contain genomic regions corresponding to the `anchor*.id` values.

### Details

This function facilitates the input of processed Hi-C data from other sources into the current pipeline. Each row of `x` corresponds to a read pair, and each entry in `x$anchor1.id` and `x$anchor2.id` contains an index for `param$fragments`. Thus, the pair of indices for each row denotes the the interacting regions for each read pair. These regions are generally expected to be restriction fragments in conventional Hi-C experiments.

Obviously, the coordinates of the restriction fragment boundaries in `param$fragments` should correspond to the genome to which the reads were aligned. These can be generated using the `cutGenome` function from any given `BSgenome` object or the FASTA files used for alignment. Values of `param$discard` and `param$restrict` will not be used here and can be ignored.

Any additional fields in `x` will also be saved to file. Users are recommended to put in `anchor1.pos`, `anchor1.len`, `anchor2.pos` and `anchor2.len` fields. These should mimic the output of `preparePairs`:

`anchorY.pos`:

  Integer field, containing the 1-based genomic position of the left-most aligned base of read Y.

`anchorY.len`:

  Integer field, containing the length of the alignment of read Y on the reference sequence. This should be multiplied by -1 if the alignment was on the negative strand.

These fields enable the use of more diffHic functions, e.g., removal of reads in `param$discard` during counting with `squareCounts`, correct calculation of statistics with `getPairData`, quality control with `prunePairs`.

For storing DNase Hi-C data, `param$fragments` should be empty but the `seqinfo` should contain the lengths and names of all chromosomes. Here, the input `anchor1.id` and `anchor2.id` should contain indices of the `seqlengths`. This specifies the chromosome to which each read is aligned, e.g., an `anchor1.id` of 2 means that read 1 is aligned to the second chromosome in `seqlengths`. Note that, for this type of data, it is essential to store the position and length fields mentioned above.

When constructing the output file, `x` will be resorted by `anchor1.id`, then `anchor2.id`. If necessary, anchor1 and anchor2 indices will be switched such that the former is never less than the latter. For DNase Hi-C data, both of these fields will ultimately be set to zero - see `prepPseudoPairs` for more details.

### Value

An index file is produced at the specified `file` location, containing the interaction data. A `NULL` value is invisibly returned.

### Author(s)

Aaron Lun

### See Also

`preparePairs`, `cutGenome`

### Examples

    hic.file <- system.file("exdata", "hic_sort.bam", package="diffHic")
    cuts <-readRDS(system.file("exdata", "cuts.rds", package="diffHic"))
    param <- pairParam(cuts)

    n <- 1000
    all.a <- as.integer(runif(n, 1L, length(cuts)))
    all.t <- as.integer(runif(n, 1L, length(cuts)))
    x <- data.frame(anchor1.id=all.a, anchor2.id=all.t,
    	anchor1.pos=runif(1:100), anchor1.len=10,
    	anchor2.pos=runif(1:100), anchor2.len=-10)

    # Note: don't save to a temporary file for actual data.
    fout <- tempfile(fileext=".h5")
    savePairs(x, fout, param)
    require(rhdf5)
    head(h5read(fout, "chrA/chrA"))

[Package diffHic version 1.18.0 Index]