VCFloci | R Documentation |
These functions help to extract information from VCF files and to
select which loci to read with read.vcf
.
VCFloci(file, what = "all", chunk.size = 1e9, quiet = FALSE)
## S3 method for class 'VCFinfo'
print(x, ...)
VCFheader(file)
VCFlabels(file)
## S3 method for class 'VCFinfo'
is.snp(x)
rangePOS(x, from, to)
selectQUAL(x, threshold = 20)
getINFO(x, what = "DP", as.is = FALSE)
file |
file name of the VCF file. |
what |
a character specifying the information to be extracted (see details). |
chunk.size |
the size of data in bytes read at once. |
quiet |
a logical: should the progress of the operation be printed? |
x |
an object of class |
from , to |
integer values giving the range of position values. |
threshold |
a numerical value indicating the minimum value of quality for selecting loci. |
as.is |
a logical. By default, |
... |
further arguments passed to and from other methods. |
The variant call format (VCF) is described in details in the References. Roughly, a VCF file is made of two parts: the header and the genotypes. The last line of the header gives the labels of the genotypes: the first nine columns give information for each locus and are (always) "CHROM", "POS", "ID", "REF", "ALT", "QUAL", "FILTER", "INFO", and "FORMAT". The subsequent columns give the labels (identifiers) of the individuals; these may be missing if the file records only the variants. Note that the data are arranged as the transpose of the usual way: the individuals are as columns and the loci are as rows.
VCFloci
is the main function documented here: it reads the
information relative to each locus. The option what
specifies
which column(s) to read. By default, all of them are read. If the user
is interested in only the locus positions, the option what =
"POS"
would be used.
Since VCF files can be very big, the data are read in portions of
chunk.size
bytes. The default (1 Gb) should be appropriate in
most situations. This value should not exceed 2e9.
VCFheader
returns the header of the VCF file (excluding the
line of labels). VCFlabels
returns the individual labels.
The output of VCFloci
is a data frame with as many rows as
there are loci in the VCF file and storing the requested
information. The other functions help to extract specific information
from this data frame: their outputs may then be used to select which
loci to read with read.vcf
.
is.snp
tests whether each locus is a SNP (i.e., the reference
allele, REF, is a single charater and the alternative allele, ALT,
also). It returns a logical vector with as many values as there are
loci. Note that some VCF files have the information VT (variant type)
in the INFO column.
rangePOS
and selectQUAL
select some loci with respect to
values of position or quality. They return the indices (i.e., row
numbers) of the loci satisfying the conditions.
getINFO
extracts a specific information from the INFO
column. By default, these are the total depths (DP) which can be
changed with the option what
. The meaning of these information
should be described in the header of the VCF file.
VCFloci
returns an object of class "VCFinfo"
which is a
data frame with a specific print method.
VCFheader
returns a single character string which can be
printed nicely with cat
.
VCFlabels
returns a vector of mode character.
is.snp
returns a vector of mode logical.
rangePOS
and selectQUAL
return a vector of mode
numeric.
getINFO
returns a vector of mode character or numeric (see above).
VCFloci
is able to read either compressed (*.gz) or
uncompressed files.
Emmanuel Paradis
https://www.internationalgenome.org/wiki/Analysis/vcf4.0
https://github.com/samtools/hts-specs
read.vcf
## see ?read.vcf
Add the following code to your website.
For more information on customizing the embed code, read Embedding Snippets.