Adding studentt_cdf UDF (GoogleCloudPlatform#421)

* Adding studentt_cdf udf

* Fixed argument types

* Fixed sample number values

* Removed formatting changes

udfs/community/README.md

@@ -162,6 +162,7 @@ SELECT bqutil.fn.int(1.684)
 * [random_int](#random_intmin-any-type-max-any-type)
 * [random_string](#random_stringlength-int64)
 * [random_value](#random_valuearr-any-type)
+* [studentt_cdf](#studentt_cdfx-float64-dof-float64)
 * [sure_cond](#sure_cond)
 * [sure_like](#sure_like)
 * [sure_nonnull](#sure_nonnull)
@@ -2356,3 +2357,21 @@ Results:
 | Row	| normal_cdf |
 |-----|-------------------|
 | 1	| 0.3820885778110474 |
+
+---
+
+### [studentt_cdf(x FLOAT64, dof FLOAT64)](studentt_cdf.sqlx)
+
+Returns the value of x in the cdf of the Student's T distribution with dof degrees of freedom.
+
+Sample Query:
+
+```SQL
+SELECT `bqutils.fn.studentt_cdf`(1.0, 2.0) as studentt_cdf;
+```
+
+Results:
+
+| Row | studentt_cdf      |
+| --- | ----------------- |
+| 1   | 0.788675134594813 |

udfs/community/studentt_cdf.sqlx

@@ -0,0 +1,28 @@
+config { hasOutput: true }
+
+/*
+ * Copyright 2021 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+
+CREATE OR REPLACE FUNCTION ${self()}(x FLOAT64, dof FLOAT64)
+RETURNS FLOAT64
+LANGUAGE js AS """
+  return jstat['jStat']['studentt']['cdf']( x, dof )
+"""
+OPTIONS (
+	    library=["${JS_BUCKET}/jstat-v1.9.4.min.js"]
+);
+

udfs/community/test_cases.js

@@ -1205,6 +1205,15 @@ generate_udf_test("normal_cdf", [
 	expected_output: `CAST(0.3820885778110474 AS FLOAT64)`
     },
 ]);
+generate_udf_test("studentt_cdf", [
+    {
+        inputs: [
+		`CAST(1.0 AS FLOAT64)`,
+		`CAST(2.0 AS FLOAT64)`
+	],
+	expected_output: `CAST(0.788675134594813 AS FLOAT64)`
+    },
+]);
 //
 // End of StatsLib work tests
 //