Someone please help me. After applying sortSeqlevels on a GRanges object, the ranges are not sorted.

> class(a)
[1] "GRanges"
attr(,"package")
[1] "GenomicRanges"
> a
GRanges object with 10 ranges and 4 metadata columns:
       seqnames                 ranges strand | sampleName     median      mean
          <Rle>              <IRanges>  <Rle> |   <factor>  <numeric> <numeric>
   [1]        1 [ 12978123,  13001479]      * |    T127192 -1.0000000   -1.3819
   [2]       16 [ 66757067,  66862007]      * |   TBM12913  0.9021002    0.7706
   [3]        6 [153308946, 153311149]      * |      T3503 -0.9817280   -1.1798
   [4]        7 [ 44076308,  44081461]      * |        T34 -0.8688574   -1.1203
   [5]        Y [ 21477864,  24457072]      * |      T2765 -2.5616377   -2.4304
   [6]       10 [ 51361667,  51371756]      * |    T129795 -5.3192409   -4.2112
   [7]       15 [100330954, 100348572]      * |   TBM12913 -0.9999975   -1.3341
   [8]       10 [105882524, 105963528]      * |     T74139  0.4485208    0.5094
   [9]       22 [ 42522572,  42546862]      * |     T10380 -0.9801241   -1.1755
  [10]       11 [ 77531568,  77633436]      * |    T130307  0.6735005    0.6745
                CN
       <character>
   [1]         CN1
   [2]         CN3
   [3]         CN1
   [4]         CN1
   [5]         CN0
   [6]         CN0
   [7]         CN1
   [8]         CN3
   [9]         CN1
  [10]         CN3
  -------
  seqinfo: 24 sequences from an unspecified genome; no seqlengths
> sortSeqlevels(a)
GRanges object with 10 ranges and 4 metadata columns:
       seqnames                 ranges strand | sampleName     median      mean
          <Rle>              <IRanges>  <Rle> |   <factor>  <numeric> <numeric>
   [1]        1 [ 12978123,  13001479]      * |    T127192 -1.0000000   -1.3819
   [2]       16 [ 66757067,  66862007]      * |   TBM12913  0.9021002    0.7706
   [3]        6 [153308946, 153311149]      * |      T3503 -0.9817280   -1.1798
   [4]        7 [ 44076308,  44081461]      * |        T34 -0.8688574   -1.1203
   [5]        Y [ 21477864,  24457072]      * |      T2765 -2.5616377   -2.4304
   [6]       10 [ 51361667,  51371756]      * |    T129795 -5.3192409   -4.2112
   [7]       15 [100330954, 100348572]      * |   TBM12913 -0.9999975   -1.3341
   [8]       10 [105882524, 105963528]      * |     T74139  0.4485208    0.5094
   [9]       22 [ 42522572,  42546862]      * |     T10380 -0.9801241   -1.1755
  [10]       11 [ 77531568,  77633436]      * |    T130307  0.6735005    0.6745
                CN
       <character>
   [1]         CN1
   [2]         CN3
   [3]         CN1
   [4]         CN1
   [5]         CN0
   [6]         CN0
   [7]         CN1
   [8]         CN3
   [9]         CN1
  [10]         CN3
  -------
  seqinfo: 24 sequences from an unspecified genome; no seqlengths

> sessionInfo()
R version 3.3.3 (2017-03-06)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: openSUSE 13.1 (Bottle) (x86_64)

locale:
 [1] LC_CTYPE=en_GB.UTF-8       LC_NUMERIC=C
 [3] LC_TIME=en_GB.UTF-8        LC_COLLATE=en_GB.UTF-8
 [5] LC_MONETARY=en_GB.UTF-8    LC_MESSAGES=en_GB.UTF-8
 [7] LC_PAPER=en_GB.UTF-8       LC_NAME=C
 [9] LC_ADDRESS=C               LC_TELEPHONE=C
[11] LC_MEASUREMENT=en_GB.UTF-8 LC_IDENTIFICATION=C

attached base packages:
[1] stats4    parallel  stats     graphics  grDevices utils     datasets
[8] methods   base

other attached packages:
[1] Biobase_2.34.0       BiocInstaller_1.24.0 rtracklayer_1.34.2
[4] cn.mops_1.20.1       GenomicRanges_1.26.4 GenomeInfoDb_1.10.3
[7] IRanges_2.8.2        S4Vectors_0.12.2     BiocGenerics_0.20.0

loaded via a namespace (and not attached):
 [1] lattice_0.20-35            XML_3.98-1.9
 [3] Rsamtools_1.26.2           Biostrings_2.42.1
 [5] snow_0.4-2                 GenomicAlignments_1.10.1
 [7] bitops_1.0-6               grid_3.3.3
 [9] exomeCopy_1.20.0           zlibbioc_1.20.0
[11] XVector_0.14.1             Matrix_1.2-10
[13] BiocParallel_1.8.2         tools_3.3.3
[15] RCurl_1.95-4.8             SummarizedExperiment_1.4.0

That's expected. It only sorts the seqlevels, not the ranges. To sort the ranges, call sort(a) after calling sortSeqlevels(), but note that will sort by more than just the seqnames.