染色体坐标排序

绘图的时候经常会遇到这个问题，有些NGS软件也会遇到

通常默认的排序：

[1] "chr1"  "chr10" "chr11" "chr12" "chr13" "chr14" "chr15" "chr16"
 [9] "chr17" "chr18" "chr19" "chr2"  "chr3"  "chr4"  "chr5"  "chr6" 
[17] "chr7"  "chr8"  "chr9" 

这种情况下sort是没有意义的。

可以通过在数字前面补0来，如果有X,Y染色体，可以转换为数值

  chr=  paste('chr',
              sprintf('%02d',as.numeric(gsub('chr','',pos_df$chr))) ,
                      sep = '') 

修改后再次sort如下：

[1] "chr01" "chr02" "chr03" "chr04" "chr05" "chr06" "chr07" "chr08"
 [9] "chr09" "chr10" "chr11" "chr12" "chr13" "chr14" "chr15" "chr16"
[17] "chr17" "chr18" "chr19"