From b0401e8b69c116f7fe99b4a5889f4ca9eab9ae44 Mon Sep 17 00:00:00 2001
From: gqcolli <gqcolli@sandia.gov>
Date: Fri, 7 Nov 2025 14:45:31 -0700
Subject: [PATCH 1/2] use numpy to export/import sparse tensors

---
 pyttb/export_data.py | 15 +++++----------
 pyttb/import_data.py | 15 ++++++---------
 2 files changed, 11 insertions(+), 19 deletions(-)

diff --git a/pyttb/export_data.py b/pyttb/export_data.py
index 520e89a2..15f18add 100644
--- a/pyttb/export_data.py
+++ b/pyttb/export_data.py
@@ -100,7 +100,7 @@ def export_sparse_size(fp: TextIO, A: ttb.sptensor):
     print(f"{len(A.shape)}", file=fp)  # # of dimensions on one line
     shape_str = " ".join([str(d) for d in A.shape])
     print(f"{shape_str}", file=fp)  # size of each dimensions on the next line
-    print(f"{A.nnz}", file=fp)  # number of nonzeros
+    print(f"{A.nnz}", file=fp)  # number of nonzeros (could eliminate)
 
 
 def export_sparse_array(
@@ -109,12 +109,7 @@ def export_sparse_array(
     """Export sparse array data in coordinate format."""
     if not fmt_data:
         fmt_data = "%.16e"
-    # TODO: looping through all values may take a long time, can this be more efficient?
-    for i in range(A.nnz):
-        # 0-based indexing in package, 1-based indexing in file
-        subs = A.subs[i, :] + index_base
-        subs.tofile(fp, sep=" ", format="%d")
-        print(end=" ", file=fp)
-        val = A.vals[i][0]
-        val.tofile(fp, sep=" ", format=fmt_data)
-        print(file=fp)
+    # 0-based indexing in package, 1-based indexing in file
+    subs = A.subs + index_base
+    vals = A.vals[:, 0].reshape(-1, 1)
+    np.savetxt(fp, np.hstack((subs, vals)), fmt="%d " * subs.shape[1] + fmt_data)
diff --git a/pyttb/import_data.py b/pyttb/import_data.py
index 7c73c26d..757c87f1 100644
--- a/pyttb/import_data.py
+++ b/pyttb/import_data.py
@@ -46,8 +46,8 @@ def import_data(
 
         if data_type == "sptensor":
             shape = import_shape(fp)
-            nz = import_nnz(fp)
-            subs, vals = import_sparse_array(fp, len(shape), nz, index_base)
+            _ = import_nnz(fp)  # Could remove this line from export
+            subs, vals = import_sparse_array(fp, index_base)
             return ttb.sptensor(subs, vals, shape)
 
         if data_type == "matrix":
@@ -96,15 +96,12 @@ def import_rank(fp: TextIO) -> int:
 
 
 def import_sparse_array(
-    fp: TextIO, n: int, nz: int, index_base: int = 1
+    fp: TextIO, index_base: int = 1
 ) -> tuple[np.ndarray, np.ndarray]:
     """Extract sparse data subs and vals from coordinate format data."""
-    subs = np.zeros((nz, n), dtype="int64")
-    vals = np.zeros((nz, 1))
-    for k in range(nz):
-        line = fp.readline().strip().split(" ")
-        subs[k, :] = [np.int64(i) - index_base for i in line[:-1]]
-        vals[k, 0] = line[-1]
+    data = np.loadtxt(fp)
+    subs = data[:, :-1].astype("int64") - index_base
+    vals = data[:, -1].reshape(-1, 1)
     return subs, vals
 
 

From d974d5c449bdb908f05552ac7f6929eb1256a821 Mon Sep 17 00:00:00 2001
From: gqcolli <gqcolli@sandia.gov>
Date: Fri, 14 Nov 2025 10:03:43 -0700
Subject: [PATCH 2/2] check imported tensor dimensions

---
 pyttb/export_data.py |  2 +-
 pyttb/import_data.py | 10 +++++++---
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/pyttb/export_data.py b/pyttb/export_data.py
index 15f18add..09dd3d36 100644
--- a/pyttb/export_data.py
+++ b/pyttb/export_data.py
@@ -100,7 +100,7 @@ def export_sparse_size(fp: TextIO, A: ttb.sptensor):
     print(f"{len(A.shape)}", file=fp)  # # of dimensions on one line
     shape_str = " ".join([str(d) for d in A.shape])
     print(f"{shape_str}", file=fp)  # size of each dimensions on the next line
-    print(f"{A.nnz}", file=fp)  # number of nonzeros (could eliminate)
+    print(f"{A.nnz}", file=fp)  # number of nonzeros
 
 
 def export_sparse_array(
diff --git a/pyttb/import_data.py b/pyttb/import_data.py
index 757c87f1..c31cc167 100644
--- a/pyttb/import_data.py
+++ b/pyttb/import_data.py
@@ -46,8 +46,8 @@ def import_data(
 
         if data_type == "sptensor":
             shape = import_shape(fp)
-            _ = import_nnz(fp)  # Could remove this line from export
-            subs, vals = import_sparse_array(fp, index_base)
+            nz = import_nnz(fp)
+            subs, vals = import_sparse_array(fp, len(shape), nz, index_base)
             return ttb.sptensor(subs, vals, shape)
 
         if data_type == "matrix":
@@ -96,12 +96,16 @@ def import_rank(fp: TextIO) -> int:
 
 
 def import_sparse_array(
-    fp: TextIO, index_base: int = 1
+    fp: TextIO, n: int, nz: int, index_base: int = 1
 ) -> tuple[np.ndarray, np.ndarray]:
     """Extract sparse data subs and vals from coordinate format data."""
     data = np.loadtxt(fp)
     subs = data[:, :-1].astype("int64") - index_base
     vals = data[:, -1].reshape(-1, 1)
+    if subs.shape[0] != nz:
+        raise ValueError("Imported nonzeros are not of expected size")
+    if subs.shape[1] != n:
+        raise ValueError("Imported tensor is not of expected shape")
     return subs, vals