samtools arror: [E::hts_idx_push] NO_COOR reads not in a single block at the end 0 -1

Question

[marongiu.luigi]

Dear all,

I have aligned a file with the command:

bwa mem -t 10 <refFile> <input_1.fq.gz> <input_2.fq.gz> -o <output>.sam

then I converted the SAM to BAM with:

samtools view -Sb  <output>.sam   > <output>.bam

and I wanted to make the index of it with:

samtools index <output>.bam

but I got the error:

[E::hts_idx_push] NO_COOR reads not in a single block at the end 0 -1 samtools index: failed to create index for "output.bam"

To check if the error was due to missing alignment I checked the number of mapped reads with:

samtools -c -F 4 <output>.bam

but I got the error:

[main] unrecognized command '-c'

and when removing the flag -c I got:

samtools -F 4 <output>.bam

[main] unrecognized command '-F'

Why I got the [E::hts_idx_push] error? maybe a missing heading?

And why the flags are not recognized?

Thank you.

Answer 1

[ATpoint]

There are two things:

1) Indexing requires coordinate-sorted files.

bwa mem idx file_1.fq.gz file_2.fq.gz | samtools sort -o file_sorted.bam -
samtools index file_sorted.bam

Directly pipe the sam file to the sort, there is no need to keep the uncompressed and unsorted sam files. They only take up space.

2) Your -c -f -F etc... commands must be used like samtools view -f -F -c (...). You did not specify the subcommand they belong to.

[marongiu.luigi]

thanks, you are right, now it works!

[ATpoint]

If the answer helped you, please consider to mark it as accepted to help others in the future.

[Kevin Blighe]

Well done bro!