readCdfUnitsWriteMap: Generates an Affymetrix cell-index write map from a CDF file
In affxparser: Affymetrix File Parsing SDK

Description Usage Arguments Value Author(s) See Also Examples

Generates an Affymetrix cell-index write map from a CDF file.

The purpose of this method is to provide a re-ordering of cell elements such that cells in units (probesets) can be stored in contiguous blocks. When reading cell elements unit by unit, minimal file re-position is required resulting in a faster reading.

Note: At the moment does this package not provide methods to write/reorder CEL files. In the meanwhile, you have to write and re-read using your own file format. That's not too hard using writeBin() and readBin().

1	readCdfUnitsWriteMap(filename, units=NULL, ..., verbose=FALSE)

`filename`	The pathname of the CDF file.
`units`	An `integer` `vector` of unit indices specifying which units to listed first. All other units are added in order at the end. If `NULL`, units are in order.
`...`	Additional arguments passed to `readCdfUnits`().
`verbose`	Either a `logical`, a `numeric`, or a `Verbose` object specifying how much verbose/debug information is written to standard output. If a Verbose object, how detailed the information is is specified by the threshold level of the object. If a numeric, the value is used to set the threshold of a new Verbose object. If `TRUE`, the threshold is set to -1 (minimal). If `FALSE`, no output is written (and neither is the R.utils package required).

A integer vector which is a write map.

Henrik Bengtsson

To invert maps, see invertMap(). readCel() and readCelUnits().

  ##############################################################
if (require("AffymetrixDataTestFiles")) {            # START #
##############################################################

# Find any CDF file
cdfFile <- findCdf()

# Create a cell-index map (for writing)
writeMap <- readCdfUnitsWriteMap(cdfFile)

# Inverse map to be used to read cell elements such that, when read
# read unit by unit, they are read much faster.
readMap <- invertMap(writeMap)

# Validate the two maps
stopifnot(identical(readMap[writeMap], 1:length(readMap)))


cat("Summary of the \"randomness\" of the cell indices:\n")
moves <- diff(readMap) - 1
cat(sprintf("Number of unnecessary file re-positioning: %d (%.1f%%)\n",
                   sum(moves != 0), 100*sum(moves != 0)/length(moves)))
cat(sprintf("Extra positioning: %.1fGb\n", sum(abs(moves))/1024^3))

smallMoves <- moves[abs(moves) <= 25];
largeMoves <- moves[abs(moves)  > 25];
layout(matrix(1:2))
main <- "Non-signed file moves required in unorded file"
hist(smallMoves, nclass=51, main=main, xlab="moves <=25 bytes")
hist(largeMoves, nclass=101, main="", xlab="moves >25 bytes")

# Clean up
layout(1)
rm(cdfFile, readMap, writeMap, moves, smallMoves, largeMoves, main)

##############################################################
}                                                     # STOP #
##############################################################



  ##############################################################
if (require("AffymetrixDataTestFiles")) {            # START #
##############################################################

# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
# Function to read Affymetrix probeset annotations
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
readAffymetrixProbesetAnnotation <- function(pathname, ...) {
  # Get headers
  header <- scan(pathname, what="character", sep=",", quote="\"",
                                                      quiet=TRUE, nlines=1);

  # Read only a subset of columns (unique to this example)
  cols <- c("Probe Set ID"="probeSet",
            "Chromosome"="chromosome",
            "Physical Position"="physicalPosition",
            "dbSNP RS ID"="dbSnpId");

  colClasses <- rep("NULL", length(header));
  colClasses[header %in% names(cols)] <- "character";

  # Read the data (this is what takes time)
  df <- read.table(pathname, colClasses=colClasses, header=TRUE, sep=",",
         quote="\"", na.strings="---", strip.white=TRUE, check.names=FALSE,
                 blank.lines.skip=FALSE, fill=FALSE, comment.char="", ...);

  # Re-order columns
  df <- df[,match(names(cols),colnames(df))];
  colnames(df) <- cols;

  # Use "Probe Set ID" as rownames. Note that if we use 'row.names=1'
  # or similar something goes wrong. /HB 2006-03-06
  rownames(df) <- df[[1]];
  df <- df[,-1]; 

  # Change types of columns
  df[[1]] <- factor(df[[1]], levels=c(1:22,"X","Y",NA), ordered=TRUE);
  df[[2]] <- as.integer(df[[2]]);

  df;
} # readAffymetrixProbesetAnnotation()



# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
# Main
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
for (zz in 1) {
# Chip to be remapped
chipType <- "Mapping50K_Xba240"

annoFile <- paste(chipType, "_annot.csv", sep="")
cdfFile <- findCdf(chipType)
if (is.null(cdfFile) || !file.exists(annoFile))
  break;

# Read SNP location details
snpInfo <- readAffymetrixProbesetAnnotation(annoFile)

# Order by chromsome and then physical position
o <- order(snpInfo[[1]], snpInfo[[2]])
snpInfo <- snpInfo[o,]
rm(o)

# Read unit names in CDF file
unitNames <- readCdfUnitNames(cdfFile)

# The CDF unit indices sorted by chromsomal position
units <- match(rownames(snpInfo), unitNames)

# ...and cell indices in the same order
writeMap <- readCdfUnitsWriteMap(cdfFile, units=units)

# Inverse map to be used to write cell elements such that, if they
# later are read unit by unit, they are read in contiguous blocks.
readMap <- invertMap(writeMap)

# Clean up
rm(chipType, annoFile, cdfFile, snpInfo, unitNames, units, readMap, writeMap)

} # for (zz in 1)
##############################################################
}                                                     # STOP #
##############################################################