get subset of table based on unique column values - bash

Question

H- I am looking for a bash/awk/sed solution to get subsets of a table based on unique column values. For example if I have:
chrom1 333
chrom1 343
chrom2 380
chrom2 501
chrom1 342
chrom3 102
I want to be able to split this table into 3:
chrom1 333
chrom1 343
chrom1 342
chrom2 380
chrom2 501
chrom3 102
I know how to do this in R using the split command, but I am specifically looking for a bash/awk/sed solution.
Thanks

Answer 1

I don’t know if this awk is of any use but it will create 3 separate file based on the unique column values:
awk '{print >> $1; close($1)}' file

Answer 2

alternative awk which keeps the original order of records within each block
$ awk '{a[$1]=a[$1]?a[$1] ORS $0:$0}
END{for(k in a) print a[k] ORS ORS}' file
generates
chrom1 333
chrom1 343
chrom1 342
chrom2 380
chrom2 501
chrom3 102
there are 2 trailing empty lines at the end but not displayed in the formatted output.

Answer 3

Using sort and awk:
sort -k1,1 file | awk 'NR>1 && p != $1{print ORS} {p=$1} 1'
EDIT: If you want to keep original order of records from input file then use:
awk -v ORS='\n\n' '!($1 in a){a[$1]=$0; ind[++i]=$1; next}
{a[$1]=a[$1] RS $0}
END{for(k=1; k<=i; k++) print a[ind[k]]}' file

Answer 4

create input list file.txt
(
cat << EOF
chrom1 333
chrom1 343
chrom2 380
chrom2 501
chrom1 342
chrom3 102
EOF
) > file.txt
transfomation
cat file.txt | cut -d" " -f1 | sort -u | while read c
do
cat file.txt | grep "^$c" | sort
echo
done