add nextflow d30e48d

nextflow/docs/snippets/grouptuple-groupkey.nf

@@ -0,0 +1,13 @@
+channel.of(
+        ['chr1', ['/path/to/region1_chr1.vcf', '/path/to/region2_chr1.vcf']],
+        ['chr2', ['/path/to/region1_chr2.vcf', '/path/to/region2_chr2.vcf', '/path/to/region3_chr2.vcf']],
+    )
+    .flatMap { chr, vcfs ->
+        vcfs.collect { vcf ->
+            tuple(groupKey(chr, vcfs.size()), vcf)              // preserve group size with key
+        }
+    }
+    .view { v -> "scattered: ${v}" }
+    .groupTuple()
+    .map { key, vcfs -> tuple(key.getGroupTarget(), vcfs) }     // unwrap group key
+    .view { v -> "gathered: ${v}" }