I have one simple goal:

gr <- GRanges(seqnames = c("chr1", "chr2"),
              ranges = IRanges(start = 1:2, end = 4:5))

I want to change the chromosome names all to "chrX"

> seqnames(gr) <- "chrX"
Error in .normalize_seqnames_replacement_value(value, x) : 
  levels of supplied 'seqnames' must be identical to 'seqlevels(x)'

Please let me know if there is a simple way to do this.

Best regards

I can't imagine the use case for doing that, but it's easy enough to do. You just can't do it to the original GRanges object, so far as I know. But you can make a new one easily enough.

> gr <- GRanges(seqnames = c("chr1", "chr2"),
              ranges = IRanges(start = 1:2, end = 4:5))

> gr
GRanges object with 2 ranges and 0 metadata columns:
      seqnames    ranges strand
         <Rle> <IRanges>  <Rle>
  [1]     chr1       1-4      *
  [2]     chr2       2-5      *
  -------
  seqinfo: 2 sequences from an unspecified genome; no seqlengths
> gr2 <- GRanges(rep("chrx", length(gr)), ranges(gr))
> gr2
GRanges object with 2 ranges and 0 metadata columns:
      seqnames    ranges strand
         <Rle> <IRanges>  <Rle>
  [1]     chrx       1-4      *
  [2]     chrx       2-5      *
  -------
  seqinfo: 1 sequence from an unspecified genome; no seqlengths