Dear all,

I've been trying to use tracks() function from ggbio to combine several genomic tracks, but it seems that whenever you combine them, the x axis does not keep the original scale. The x axis coordinates and ticks do even change when the order of the plots is a different one. Below you can find the code for an example that shows my problem. If you look at the x axis of the first combined plot (combined_tracks1), it is completely different to the x axis of the second combined plot (combined_tracks2), although they both should look the same way, but only with the two plots in the reverse order.

library(ggbio）

test_a = GRanges('chr1', IRanges(start = 150, end = 180))
t_a <- autoplot(test_a)
t_a

test_b = GRanges('chr1', IRanges(start = 100, end = 200))
t_b <- autoplot(test_b)
t_b

## ORDER A, B
combined_tracks1 <-   tracks(t_a, t_b)      
combined_tracks1

## ORDER B, A
combined_tracks2 <-   tracks(t_b, t_a)      
combined_tracks2

combined_tracks1

combined_tracks2

sessionInfo()

R version 3.3.1 (2016-06-21)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 7 x64 (build 7601) Service Pack 1

locale:
[1] LC_COLLATE=English_United States.1252  LC_CTYPE=English_United States.1252    LC_MONETARY=English_United States.1252
[4] LC_NUMERIC=C                           LC_TIME=English_United States.1252    

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

other attached packages:
 [1] SNPlocs.Hsapiens.dbSNP142.GRCh37_0.99.5 VariantAnnotation_1.18.7                Rsamtools_1.24.0                       
 [4] SummarizedExperiment_1.2.3              BSgenome.Hsapiens.UCSC.hg19_1.4.0       BSgenome_1.40.1                        
 [7] Biostrings_2.40.2                       XVector_0.12.1                          rtracklayer_1.32.2                     
[10] cowplot_0.6.2                           scales_0.4.0                            plyr_1.8.4                             
[13] reshape_0.8.5                           Homo.sapiens_1.3.1                      TxDb.Hsapiens.UCSC.hg19.knownGene_3.2.2
[16] org.Hs.eg.db_3.3.0                      GO.db_3.3.0                             OrganismDbi_1.14.1                     
[19] GenomicFeatures_1.24.5                  AnnotationDbi_1.34.4                    Biobase_2.32.0                         
[22] GenomicRanges_1.24.2                    GenomeInfoDb_1.8.3                      IRanges_2.6.1                          
[25] S4Vectors_0.10.3                        biovizBase_1.20.0                       ggbio_1.20.2                           
[28] ggplot2_2.1.0                           BiocGenerics_0.18.0                    

loaded via a namespace (and not attached):
 [1] httr_1.2.1                    AnnotationHub_2.4.2           splines_3.3.1                 Formula_1.2-1                
 [5] shiny_0.13.2                  interactiveDisplayBase_1.10.3 latticeExtra_0.6-28           RBGL_1.48.1                  
 [9] RSQLite_1.0.0                 lattice_0.20-33               chron_2.3-47                  digest_0.6.10                
[13] RColorBrewer_1.1-2            colorspace_1.2-6              htmltools_0.3.5               httpuv_1.3.3                 
[17] Matrix_1.2-6                  XML_3.98-1.4                  biomaRt_2.28.0                zlibbioc_1.18.0              
[21] xtable_1.8-2                  BiocParallel_1.6.6            nnet_7.3-12                   survival_2.39-5              
[25] magrittr_1.5                  mime_0.5                      GGally_1.2.0                  foreign_0.8-66               
[29] graph_1.50.0                  BiocInstaller_1.22.3          tools_3.3.1                   data.table_1.9.6             
[33] stringr_1.1.0                 munsell_0.4.3                 cluster_2.0.4                 ensembldb_1.4.7              
[37] grid_3.3.1                    RCurl_1.95-4.8                dichromat_2.0-0               bitops_1.0-6                 
[41] labeling_0.3                  gtable_0.2.0                  DBI_0.5                       reshape2_1.4.1               
[45] R6_2.1.3                      GenomicAlignments_1.8.4       gridExtra_2.2.1               Hmisc_3.17-4                 
[49] stringi_1.1.1                 Rcpp_0.12.6                   rpart_4.1-10                  acepack_1.3-3.3          

I have the answer to my own question.

You need to fix the x axis for each of your single plots like this:

library(ggbio）

test_a = GRanges('chr1', IRanges(start = 150, end = 180))
t_a <- autoplot(test_a)  + xlim (100, 200)
t_a
fixed(t_a) <- TRUE

test_b = GRanges('chr1', IRanges(start = 100, end = 200))
t_b <- autoplot(test_b)  + xlim (100, 200)
t_b
fixed(t_b) <- TRUE

## ORDER A, B
combined_tracks1 <-   tracks(t_a, t_b) +
                        xlim (100, 200)      
combined_tracks1

## ORDER B, A
combined_tracks2 <-   tracks(t_b, t_a) +
                        xlim (100, 200)      
combined_tracks2

Hello Oswaldo,

Indeed, the tracks() function doesn't do any scaling on the provided tracks. As the manual states: "you can use this function to bind any tracks with the same defination [sic] of x axis, for example, sets of time series plots you made."

In ordner to scale your tracks consistently, you have to provide a range to be plotted via the xlim parameter to the function.

  scale_combined <- GRanges('chr1', IRanges(start = 50, end = 250))
        
        ## ORDER A, B
        combined_tracks1 <-   tracks(t_a, t_b,xlim=scale_combined)      
        combined_tracks1
        
        ## ORDER B, A
        combined_tracks2 <-   tracks(t_b, t_a,xlim=scale_combined)      
        combined_tracks2

Best

Matthias