MALDIquant (version 1.4)

binPeaks: Align Peaks into discrete bins.

Description

This function looks for similar peaks (mass) across MassPeaks objects and equalizes their mass.

Usage

binPeaks(l, method=c("strict", "relaxed"), tolerance=0.002)

Arguments

l

list, list of MassPeaks objects.

method

bin creation rule. "strict" creates bins never containing two or more peaks of the sampe sample. "relaxed" allows multiple peaks of the same sample in one bin.

tolerance

double, maximal deviation of a peak position (mass) to be considered as identical.

Value

• Returns a list of mass adjusted MassPeaks objects.

code

method == "strict"

cr

method == "relaxed": The new peak positions for the highest peaks of each sample in a bin are generated by the mean mass of this peaks. The lower peaks are not changed.

Details

The algorithm is based on the following workflow:

1. Put all mass in a sorted vector.

Calculate differences between each neighbor. Divide the mass vector at the largest gap (largest difference) and form a left and a right bin. Rerun step 3 for the left and/or the right bin if they don't fulfill the following criteria:

• All peaks in a bin are near to the mean (abs(mass-meanMass)/meanMass < tolerance).

method == "strict": The bin doesn't contain two or more peaks of the same sample.

References

See website: http://strimmerlab.org/software/maldiquant/

See Also

intensityMatrix, MassPeaks

Examples

## load library
library("MALDIquant");

## create two MassPeaks objects
p <- list(createMassPeaks(mass=seq(100, 500, 100), intensity=1:5),
          createMassPeaks(mass=c(seq(100.2, 300.2, 100), 395), intensity=1:4));

## only keep peaks which occur in all MassPeaks objects
binnedPeaks <- binPeaks(p, tolerance=0.002);

## compare result
iM1 <- intensityMatrix(p);
iM2 <- intensityMatrix(binnedPeaks);

all(dim(iM1) == c(2, 9)); # TRUE
all(dim(iM2) == c(2, 6)); # TRUE

show(iM2);

## increase tolerance
binnedPeaks <- binPeaks(p, tolerance=0.1);

iM3 <- intensityMatrix(binnedPeaks);

all(dim(iM3) == c(2, 5)); # TRUE

show(iM3);

## differences between "strict" and "relaxed"
p <- c(createMassPeaks(mass=c(1, 1.01, 3), intensity=c(2, 1, 1)),
       createMassPeaks(mass=c(0.99, 3), intensity=rep(1, 2)),
       createMassPeaks(mass=c(1.02, 3), intensity=rep(1, 2)));

intensityMatrix(binPeaks(p, method="strict", tolerance=0.05));
intensityMatrix(binPeaks(p, method="relaxed", tolerance=0.05));