From 0e1c22e1873a6cdd5a8632e524adc09cc71ed3f2 Mon Sep 17 00:00:00 2001
From: Arun Isaac
Date: Tue, 2 Sep 2025 15:59:40 +0100
Subject: Catenate an empty list of genotypes.

We handle this as a special case.
---
 pyhegp/pyhegp.py | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/pyhegp/pyhegp.py b/pyhegp/pyhegp.py
index 3ffa314..f204a36 100644
--- a/pyhegp/pyhegp.py
+++ b/pyhegp/pyhegp.py
@@ -111,7 +111,17 @@ def encrypt_genotype(genotype, key, summary):
                      axis="columns")
 
 def cat_genotype(genotypes):
-    return pd.concat(genotypes)
+    match genotypes:
+        # If there are no input data frames, return an empty data
+        # frame with the chromosome and position columns.
+        case []:
+            genotype = pd.DataFrame(data={"chromosome": [],
+                                          "position": []})
+            genotype.chromosome = genotype.chromosome.astype("str")
+            genotype.position = genotype.position.astype("int")
+            return genotype
+        case _:
+            return pd.concat(genotypes)
 
 @click.group()
 def main():
-- 
cgit 1.4.1