From 03b8fdec7481139006480e11e6be6c68803dd9c2 Mon Sep 17 00:00:00 2001
From: Alexander Gugel <alexander.gugel@gmail.com>
Date: Sat, 26 Sep 2020 10:10:12 +0100
Subject: [PATCH] Add DMatrix usage examples to c-api-demo (#5854)

* Add DMatrix usage examples to c-api-demo

* Add XGDMatrixCreateFromCSREx example

* Add XGDMatrixCreateFromCSCEx example
---
 demo/c-api/c-api-demo.c | 81 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 81 insertions(+)

diff --git a/demo/c-api/c-api-demo.c b/demo/c-api/c-api-demo.c
index 34b04ed9c..d3517da44 100644
--- a/demo/c-api/c-api-demo.c
+++ b/demo/c-api/c-api-demo.c
@@ -5,6 +5,7 @@
  * \brief A simple example of using xgboost C API.
  */
 
+#include <assert.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <xgboost/c_api.h>
@@ -84,6 +85,86 @@ int main(int argc, char** argv) {
   }
   printf("\n");
 
+  {
+    printf("Dense Matrix Example (XGDMatrixCreateFromMat): ");
+
+    const float values[] = {0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0,
+      0, 0, 1, 0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0,
+      1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0,
+      0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0,
+      1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+      1, 0, 0, 0, 0, 1, 0, 0, 0, 0};
+
+    DMatrixHandle dmat;
+    safe_xgboost(XGDMatrixCreateFromMat(values, 1, 127, 0.0, &dmat));
+
+    bst_ulong out_len = 0;
+    const float* out_result = NULL;
+
+    safe_xgboost(XGBoosterPredict(booster, dmat, 0, 0, 0, &out_len,
+          &out_result));
+    assert(out_len == 1);
+
+    printf("%1.4f \n", out_result[0]);
+    safe_xgboost(XGDMatrixFree(dmat));
+  }
+
+  {
+    printf("Sparse Matrix Example (XGDMatrixCreateFromCSREx): ");
+
+    const size_t indptr[] = {0, 22};
+    const unsigned indices[] = {1, 9, 19, 21, 24, 34, 36, 39, 42, 53, 56, 65,
+      69, 77, 86, 88, 92, 95, 102, 106, 117, 122};
+    const float data[] = {1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0,
+      1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0};
+
+    DMatrixHandle dmat;
+    safe_xgboost(XGDMatrixCreateFromCSREx(indptr, indices, data, 2, 22, 127,
+      &dmat));
+
+    bst_ulong out_len = 0;
+    const float* out_result = NULL;
+
+    safe_xgboost(XGBoosterPredict(booster, dmat, 0, 0, 0, &out_len,
+          &out_result));
+    assert(out_len == 1);
+
+    printf("%1.4f \n", out_result[0]);
+    safe_xgboost(XGDMatrixFree(dmat));
+  }
+
+  {
+    printf("Sparse Matrix Example (XGDMatrixCreateFromCSCEx): ");
+
+    const size_t col_ptr[] = {0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2,
+      2, 2, 2, 2, 3, 3, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 6, 6, 7, 7, 7, 8,
+      8, 8, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 10, 10, 10, 11, 11, 11, 11, 11, 11,
+      11, 11, 11, 12, 12, 12, 12, 13, 13, 13, 13, 13, 13, 13, 13, 14, 14, 14,
+      14, 14, 14, 14, 14, 14, 15, 15, 16, 16, 16, 16, 17, 17, 17, 18, 18, 18,
+      18, 18, 18, 18, 19, 19, 19, 19, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20,
+      20, 21, 21, 21, 21, 21, 22, 22, 22, 22, 22};
+
+    const unsigned indices[] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+      0, 0, 0, 0, 0, 0};
+
+    const float data[] = {1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0,
+      1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0};
+
+    DMatrixHandle dmat;
+    safe_xgboost(XGDMatrixCreateFromCSCEx(col_ptr, indices, data, 128, 22, 1,
+      &dmat));
+
+    bst_ulong out_len = 0;
+    const float* out_result = NULL;
+
+    safe_xgboost(XGBoosterPredict(booster, dmat, 0, 0, 0, &out_len,
+          &out_result));
+    assert(out_len == 1);
+
+    printf("%1.4f \n", out_result[0]);
+    safe_xgboost(XGDMatrixFree(dmat));
+  }
+
   // free everything
   safe_xgboost(XGBoosterFree(booster));
   safe_xgboost(XGDMatrixFree(dtrain));