How to add to a VCF file's sample information into INFO column?

Question

[wrinklypalms]

How do I add sample.id into the INFO column the way the below example does it?

recreate input/output data:

input:

  #CHROM     POS          ID REF ALT               INFO sample.id
1      1 1724503  rs33952351   C  CA  AC=2;AF=1.00;AN=2       in1
2      1 1749412 rs115507312   T   G AC=1;AF=0.500;AN=2       in1
3      1 2488153      rs4870   A   G AC=1;AF=0.500;AN=2       in1
4      1   24503           .   C  CA  AC=2;AF=1.00;AN=2       in2
5      1 1749412 rs115507312   T   G AC=2;AF=0.500;AN=2       in2
6     22 2488153       rsid2   A   G AC=1;AF=0.500;AN=2       in2
7      1 1724503           .   C   T  AC=2;AF=1.00;ZZ=T       in3
8      1 1749412 rs115507312   T   G AC=1;AF=0.500;ZZ=F       in3
9      1 2488153      rs4870   A   G AC=1;AF=0.500;ZZ=T       in3

desired output:

  #CHROM     POS          ID REF ALT                                           INFO
1      1   24503           .   C  CA               AC=2;AF=1.00;AN=2;Identified=in2
2      1 1724503  rs33952351   C  CA               AC=2;AF=1.00;AN=2;Identified=in1
3      1 1749412 rs115507312   T   G AC=1;AF=0.500;AN=2;Identified=in1,in2,in3;ZZ=F
4      1 1724503           .   C   T               AC=2;AF=1.00;ZZ=T;Identified=in3
5      1 2488153      rs4870   A   G     AC=1;AF=0.500;AN=2;Identified=in1,in3;ZZ=T
6     22 2488153       rsid2   A   G              AC=1;AF=0.500;AN=2;Identified=in2

my code:

uid<-paste(file$`#CHROM`,file$POS,file$REF,file$ALT,sep="_")
INFO<-strsplit(file$INFO,split = ";")
for (i in 1:6){
  for (j in 1:9){
    samples<-unique(file$sample.id[which(file$uid == uid[i])])
    if (length(samples) > 1) {
      INFO[[j]]<-c(INFO[[j]],paste0('Identified=',paste(samples,collapse = ",")))
    } else if (length(samples) == 1) {
      INFO[[j]]<-c(INFO[[j]],paste0('Identified=',samples))
    } else {
      break }
    INFO[[j]]<-sort(INFO[[j]])
    INFO[[j]]<-paste(INFO[[j]],collapse=";")
    file$INFO[j]<-INFO[[j]]
  }
}

I can't figure the logic out, and whatever I've tried resulted in this output:

[7] "AC=2;AF=1.00;Identified=in1;ZZ=T;Identified=in1,in2,in3;Identified=in1,in3;Identified=in2;Identified=in2;Identified=in3" 
[8] "AC=1;AF=0.500;Identified=in1;ZZ=F;Identified=in1,in2,in3;Identified=in1,in3;Identified=in2;Identified=in2;Identified=in3"
[9] "AC=1;AF=0.500;Identified=in1;ZZ=T;Identified=in1,in2,in3;Identified=in1,in3;Identified=in2;Identified=in2;Identified=in3"