Introduce startsWith Predicate

api/src/main/java/org/apache/iceberg/expressions/Evaluator.java

@@ -142,5 +142,10 @@ public <T> Boolean in(BoundReference<T> ref, Literal<T> lit) {
     public <T> Boolean notIn(BoundReference<T> ref, Literal<T> lit) {
       return !in(ref, lit);
     }
+
+    @Override
+    public Boolean startsWith(BoundReference<String> ref, Literal<String> lit) {
+      return ref.get(struct).startsWith(lit.value());
+    }
   }
 }

api/src/main/java/org/apache/iceberg/expressions/Expression.java

@@ -40,7 +40,8 @@ enum Operation {
     NOT_IN,
     NOT,
     AND,
-    OR;
+    OR,
+    STARTS_WITH;
 
     /**
      * @return the operation used when this is negated

api/src/main/java/org/apache/iceberg/expressions/ExpressionVisitors.java

@@ -97,6 +97,10 @@ public <T> R notIn(BoundReference<T> ref, Literal<T> lit) {
       return null;
     }
 
+    public R startsWith(BoundReference<String> ref, Literal<String> lit) {
+      throw new UnsupportedOperationException("Unsupported operation.");
+    }
+
     @Override
     public <T> R predicate(BoundPredicate<T> pred) {
       switch (pred.op()) {
@@ -120,6 +124,9 @@ public <T> R predicate(BoundPredicate<T> pred) {
           return in(pred.ref(), pred.literal());
         case NOT_IN:
           return notIn(pred.ref(), pred.literal());
+        case STARTS_WITH:
+          // Expressions.startsWith accepts only strings, thus type casting is done here.
+          return startsWith((BoundReference<String>) pred.ref(), (Literal<String>) pred.literal());
         default:
           throw new UnsupportedOperationException(
               "Unknown operation for predicate: " + pred.op());

api/src/main/java/org/apache/iceberg/expressions/Expressions.java

@@ -105,6 +105,10 @@ public static <T> UnboundPredicate<T> notEqual(String name, T value) {
     return new UnboundPredicate<>(Expression.Operation.NOT_EQ, ref(name), value);
   }
 
+  public static UnboundPredicate<String> startsWith(String name, String value) {
+    return new UnboundPredicate<>(Expression.Operation.STARTS_WITH, ref(name), value);
+  }
+
   public static <T> UnboundPredicate<T> predicate(Operation op, String name, T value) {
     Preconditions.checkArgument(op != Operation.IS_NULL && op != Operation.NOT_NULL,
         "Cannot create %s predicate inclusive a value", op);

api/src/main/java/org/apache/iceberg/expressions/Predicate.java

@@ -62,6 +62,8 @@ public String toString() {
         return String.valueOf(ref()) + " == " + literal();
       case NOT_EQ:
         return String.valueOf(ref()) + " != " + literal();
+      case STARTS_WITH:
+        return ref() + " startsWith \"" + literal() + "\"";
 //      case IN:
 //        break;
 //      case NOT_IN:

api/src/main/java/org/apache/iceberg/transforms/Bucket.java

@@ -113,6 +113,7 @@ public UnboundPredicate<Integer> project(String name, BoundPredicate<T> predicat
             predicate.op(), name, apply(predicate.literal().value()));
 //      case IN:
 //        return Expressions.predicate();
+      case STARTS_WITH:
       default:
         // comparison predicates can't be projected, notEq can't be projected
         // TODO: small ranges can be projected.

api/src/main/java/org/apache/iceberg/transforms/ProjectionUtil.java

@@ -189,6 +189,8 @@ static <S, T> UnboundPredicate<T> truncateArray(
         return predicate(Expression.Operation.GT_EQ, name, transform.apply(boundary));
       case EQ:
         return predicate(Expression.Operation.EQ, name, transform.apply(boundary));
+      case STARTS_WITH:
+        return predicate(Expression.Operation.STARTS_WITH, name, transform.apply(boundary));
 //        case IN: // TODO
 //          return Expressions.predicate(Operation.IN, name, transform.apply(boundary));
       default:

api/src/main/java/org/apache/iceberg/transforms/Truncate.java

@@ -213,20 +213,35 @@ public boolean canTransform(Type type) {
 
     @Override
     public UnboundPredicate<CharSequence> project(String name,
-                                                  BoundPredicate<CharSequence> pred) {
-      if (pred.op() == NOT_NULL || pred.op() == IS_NULL) {
-        return Expressions.predicate(pred.op(), name);
+                                                  BoundPredicate<CharSequence> predicate) {
+      switch (predicate.op()) {
+        case NOT_NULL:
+        case IS_NULL:
+          return Expressions.predicate(predicate.op(), name);
+        case STARTS_WITH:
+        default:
+          return ProjectionUtil.truncateArray(name, predicate, this);
       }
-      return ProjectionUtil.truncateArray(name, pred, this);
     }
 
     @Override
     public UnboundPredicate<CharSequence> projectStrict(String name,
-                                                        BoundPredicate<CharSequence> pred) {
-      if (pred.op() == NOT_NULL || pred.op() == IS_NULL) {
-        return Expressions.predicate(pred.op(), name);
+                                                        BoundPredicate<CharSequence> predicate) {
+      switch (predicate.op()) {
+        case IS_NULL:
+        case NOT_NULL:
+          return Expressions.predicate(predicate.op(), name);
+        case STARTS_WITH:
+          if (predicate.literal().value().length() < width()) {
+            return Expressions.predicate(predicate.op(), name, predicate.literal().value());
+          } else if (predicate.literal().value().length() == width()) {
+            return Expressions.equal(name, predicate.literal().value());
+          } else {
+            return null;
+          }
+        default:
+          return ProjectionUtil.truncateArrayStrict(name, predicate, this);
       }
-      return ProjectionUtil.truncateArrayStrict(name, pred, this);
     }
 
     @Override

api/src/test/java/org/apache/iceberg/expressions/TestExpressionBinding.java

@@ -34,6 +34,7 @@
 import static org.apache.iceberg.expressions.Expressions.lessThan;
 import static org.apache.iceberg.expressions.Expressions.not;
 import static org.apache.iceberg.expressions.Expressions.or;
+import static org.apache.iceberg.expressions.Expressions.startsWith;
 import static org.apache.iceberg.types.Types.NestedField.required;
 
 public class TestExpressionBinding {
@@ -131,6 +132,18 @@ public void testNot() {
     Assert.assertEquals("Should bind x correctly", 0, child.ref().fieldId());
   }
 
+  @Test
+  public void testStartsWith() {
+    StructType struct = StructType.of(required(0, "s", Types.StringType.get()));
+    Expression expr = startsWith("s", "abc");
+    Expression boundExpr = Binder.bind(struct, expr);
+    TestHelpers.assertAllReferencesBound("StartsWith", boundExpr);
+    // make sure the expression is a StartsWith
+    BoundPredicate<?> pred = TestHelpers.assertAndUnwrap(boundExpr, BoundPredicate.class);
+    Assert.assertEquals("Should be right operation", Expression.Operation.STARTS_WITH, pred.op());
+    Assert.assertEquals("Should bind s correctly", 0, pred.ref().fieldId());
+  }
+
   @Test
   public void testAlwaysTrue() {
     Assert.assertEquals("Should not change alwaysTrue",

api/src/test/java/org/apache/iceberg/transforms/TestStartsWith.java

@@ -0,0 +1,99 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ */
+
+package org.apache.iceberg.transforms;
+
+import org.apache.iceberg.PartitionSpec;
+import org.apache.iceberg.Schema;
+import org.apache.iceberg.TestHelpers;
+import org.apache.iceberg.expressions.Binder;
+import org.apache.iceberg.expressions.BoundPredicate;
+import org.apache.iceberg.expressions.Evaluator;
+import org.apache.iceberg.expressions.Expression;
+import org.apache.iceberg.expressions.False;
+import org.apache.iceberg.expressions.Literal;
+import org.apache.iceberg.expressions.Projections;
+import org.apache.iceberg.expressions.UnboundPredicate;
+import org.apache.iceberg.types.Types;
+import org.junit.Assert;
+import org.junit.Test;
+
+import static org.apache.iceberg.TestHelpers.assertAndUnwrapUnbound;
+import static org.apache.iceberg.expressions.Expressions.startsWith;
+import static org.apache.iceberg.types.Types.NestedField.optional;
+
+public class TestStartsWith {
+
+  private static final String COLUMN = "someStringCol";
+  private static final Schema SCHEMA = new Schema(optional(1, COLUMN, Types.StringType.get()));
+
+  @Test
+  public void assertTruncateProjections() {
+    PartitionSpec spec = PartitionSpec.builderFor(SCHEMA).truncate(COLUMN, 4).build();
+
+    assertProjectionInclusive(spec, startsWith(COLUMN, "ab"), "ab", Expression.Operation.STARTS_WITH);
+    assertProjectionInclusive(spec, startsWith(COLUMN, "abab"), "abab", Expression.Operation.STARTS_WITH);
+    assertProjectionInclusive(spec, startsWith(COLUMN, "ababab"), "abab", Expression.Operation.STARTS_WITH);
+
+    assertProjectionStrict(spec, startsWith(COLUMN, "ab"), "ab", Expression.Operation.STARTS_WITH);
+    assertProjectionStrict(spec, startsWith(COLUMN, "abab"), "abab", Expression.Operation.EQ);
+    assertProjectionFalse(spec, startsWith(COLUMN, "ababab"));
+  }
+
+  @Test
+  public void assertTruncateString() {
+    Truncate<String> trunc = Truncate.get(Types.StringType.get(), 2);
+    Expression expr = startsWith(COLUMN, "abcde");
+    BoundPredicate<String> boundExpr = (BoundPredicate<String>) Binder.bind(SCHEMA.asStruct(),  expr, false);
+
+    UnboundPredicate<String> projected = trunc.project(COLUMN, boundExpr);
+    Evaluator evaluator = new Evaluator(SCHEMA.asStruct(), projected);
+
+    Assert.assertTrue("startsWith(abcde, truncate(abcde,2))  => true",
+        evaluator.eval(TestHelpers.Row.of("abcde")));
+  }
+
+  private void assertProjectionInclusive(PartitionSpec spec, UnboundPredicate<?> filter,
+                                         String expectedLiteral, Expression.Operation expectedOp) {
+    Expression projection = Projections.inclusive(spec).project(filter);
+    assertProjection(spec, expectedLiteral, projection, expectedOp);
+  }
+
+  private void assertProjectionStrict(PartitionSpec spec, UnboundPredicate<?> filter,
+                                         String expectedLiteral, Expression.Operation expectedOp) {
+    Expression projection = Projections.strict(spec).project(filter);
+    assertProjection(spec, expectedLiteral, projection, expectedOp);
+  }
+
+  private void assertProjection(PartitionSpec spec, String expectedLiteral, Expression projection,
+                                Expression.Operation expectedOp) {
+    UnboundPredicate<?> predicate = assertAndUnwrapUnbound(projection);
+    Literal literal = predicate.literal();
+    Truncate<CharSequence> transform = (Truncate<CharSequence>) spec.getFieldsBySourceId(1).get(0).transform();
+    String output = transform.toHumanString((String) literal.value());
+
+    Assert.assertEquals(expectedOp, predicate.op());
+    Assert.assertEquals(expectedLiteral, output);
+  }
+
+  private void assertProjectionFalse(PartitionSpec spec, UnboundPredicate<?> filter) {
+    Expression projection = Projections.strict(spec).project(filter);
+    Assert.assertTrue(projection instanceof False);
+  }
+}