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Compare Spectra of an 'MSnExp' or 'Spectrum' instances

compareSpectra-methods.Rd

This method compares spectra (Spectrum instances) pairwise or all spectra of an experiment (MSnExp instances). Currently the comparison is based on the number of common peaks fun = "common", the Pearson correlation fun = "cor", the dot product fun = "dotproduct" or a user-defined function.

For fun = "common" the tolerance (default 25e-6) can be set and the tolerance can be defined to be relative (default relative = TRUE) or absolute (relative = FALSE). To compare spectra with fun = "cor" and fun = "dotproduct", the spectra need to be binned. The binSize argument (in Dalton) controls the binning precision. Please see bin for details.

Instead of these three predefined functions for fun a user-defined comparison function can be supplied. This function takes two Spectrum objects as the first two arguments and ... as third argument. The function must return a single numeric value. See the example section.

Methods

signature(x = "MSnExp", y = "missing", fun = "character", ...)

Compares all spectra in an MSnExp object. The ... arguments are passed to the internal functions. Returns a matrix of dimension length(x) by length(x).

signature(x = "Spectrum", y = "Spectrum", fun = "character", ...)

Compares two Spectrum objects. See the above explanation for fun and .... Returns a single numeric value.

Author

Sebastian Gibb <mail@sebastiangibb.de>

See also

bin, clean, pickPeaks, smooth, removePeaks and trimMz for other spectra processing methods.

References

Stein, S. E., & Scott, D. R. (1994). Optimization and testing of mass spectral library search algorithms for compound identification. Journal of the American Society for Mass Spectrometry, 5(9), 859-866. doi: https://doi.org/10.1016/1044-0305(94)87009-8

Lam, H., Deutsch, E. W., Eddes, J. S., Eng, J. K., King, N., Stein, S. E. and Aebersold, R. (2007) Development and validation of a spectral library searching method for peptide identification from MS/MS. Proteomics, 7: 655-667. doi: https://doi.org/10.1002/pmic.200600625

Examples

s1 <- new("Spectrum2", mz=1:10, intensity=1:10)
s2 <- new("Spectrum2", mz=1:10, intensity=10:1)
compareSpectra(s1, s2)
#> [1] 10
compareSpectra(s1, s2, fun="cor", binSize=2)
#> [1] -1
compareSpectra(s1, s2, fun="dotproduct")
#> [1] 0.5714286

## define our own (useless) comparison function (it is just a basic example)
equalLength <- function(x, y, ...) {
  return(peaksCount(x)/(peaksCount(y)+.Machine$double.eps))
}
compareSpectra(s1, s2, fun=equalLength)
#> [1] 1
compareSpectra(s1, new("Spectrum2", mz=1:5, intensity=1:5), fun=equalLength)
#> [1] 2
compareSpectra(s1, new("Spectrum2"), fun=equalLength)
#> [1] 4.5036e+16

data(itraqdata)
compareSpectra(itraqdata[1:5], fun="cor")
#>            X1        X10       X11        X12        X13
#> X1         NA 0.07147120 0.3825327 0.51883926 0.45045283
#> X10 0.0714712         NA 0.0949519 0.09966693 0.07594562
#> X11 0.3825327 0.09495190        NA 0.47739388 0.46612990
#> X12 0.5188393 0.09966693 0.4773939         NA 0.56151180
#> X13 0.4504528 0.07594562 0.4661299 0.56151180         NA