feat: Join component

haystack/preview/components/joiners/join.py

@@ -0,0 +1,47 @@
+from typing import Type
+from haystack.preview import component, default_from_dict, default_to_dict, DeserializationError
+from haystack.preview.utils import marshal_type, unmarshal_type
+
+
+@component
+class Join:
+    """
+    Simple component that joins together a group of inputs of the same type. Works with every type that supports
+    the + operator for joining, like lists, strings, etc.
+    """
+
+    def __init__(self, inputs_count: int, inputs_type: Type):
+        """
+        :param inputs_count: the number of inputs to expect.
+        :param inputs_type: the type of the inputs. Every type that supports the + operator works.
+        """
+        if inputs_count < 1:
+            raise ValueError("inputs_count must be at least 1")
+        self.inputs_count = inputs_count
+        self.inputs_type = inputs_type
+        component.set_input_types(self, **{f"input_{i}": inputs_type for i in range(inputs_count)})
+        component.set_output_types(self, output=inputs_type)
+
+    def to_dict(self):
+        return default_to_dict(self, inputs_count=self.inputs_count, inputs_type=marshal_type(self.inputs_type))
+
+    @classmethod
+    def from_dict(cls, data):
+        if not "inputs_type" in data["init_parameters"]:
+            raise DeserializationError("The inputs_type parameter for Join is missing.")
+        data["init_parameters"]["inputs_type"] = unmarshal_type(data["init_parameters"]["inputs_type"])
+        return default_from_dict(cls, data)
+
+    def run(self, **kwargs):
+        """
+        Joins together a group of inputs of the same type. Works with every type that supports the + operator,
+        like lists, strings, etc.
+        """
+        if len(kwargs) != self.inputs_count:
+            raise ValueError(f"Join expected {self.inputs_count} inputs, but got {len(kwargs)}")
+
+        values = list(kwargs.values())
+        output = values[0]
+        for values in values[1:]:
+            output += values
+        return {"output": output}

haystack/preview/utils/__init__.py

@@ -1,3 +1,4 @@
 from haystack.preview.utils.expit import expit
 from haystack.preview.utils.requests_utils import request_with_retry
 from haystack.preview.utils.filters import document_matches_filter
+from haystack.preview.utils.marshalling import marshal_type, unmarshal_type

haystack/preview/utils/marshalling.py

@@ -0,0 +1,46 @@
+from typing import Type
+import builtins
+import sys
+
+from haystack.preview import DeserializationError
+
+
+def marshal_type(type_: Type) -> str:
+    """
+    Given a type, return a string representation that can be unmarshalled.
+
+    :param type_: The type.
+    :return: Its string representation.
+    """
+    module = type_.__module__
+    if module == "builtins":
+        return type_.__name__
+    return f"{module}.{type_.__name__}"
+
+
+def unmarshal_type(type_name: str) -> Type:
+    """
+    Given the string representation of a type, return the type itself.
+
+    :param type_name: The string representation of the type.
+    :return: The type itself.
+    """
+    if "." not in type_name:
+        type_ = getattr(builtins, type_name, None)
+        if not type_:
+            raise DeserializationError(f"Could not locate builtin called '{type_name}'")
+        return type_
+
+    parts = type_name.split(".")
+    module_name = ".".join(parts[:-1])
+    type_name = parts[-1]
+
+    module = sys.modules.get(module_name, None)
+    if not module:
+        raise DeserializationError(f"Could not locate the module '{module_name}'")
+
+    type_ = getattr(module, type_name, None)
+    if not type_:
+        raise DeserializationError(f"Could not locate the type '{type_name}'")
+
+    return type_

releasenotes/notes/join-lists-1307f7872a37e238.yaml

@@ -0,0 +1,3 @@
+---
+preview:
+  - Add `Join`, a small component that can be used to join lists and other types supporting the + operator.

test/preview/components/joiner/test_join.py

@@ -0,0 +1,42 @@
+from typing import List
+
+import pytest
+
+from haystack.preview.components.joiners.join import Join
+
+
+class TestJoin:
+    @pytest.mark.unit
+    def test_join_to_dict(self):
+        comp = Join(inputs_count=2, inputs_type=str)
+        assert comp.to_dict() == {"type": "Join", "init_parameters": {"inputs_count": 2, "inputs_type": "str"}}
+
+    @pytest.mark.unit
+    def test_join_from_dict(self):
+        data = {"type": "Join", "init_parameters": {"inputs_count": 2, "inputs_type": "str"}}
+        comp = Join.from_dict(data)
+        assert comp.inputs_count == 2
+        assert comp.inputs_type == str
+
+    @pytest.mark.unit
+    def test_join_list(self):
+        comp = Join(inputs_count=2, inputs_type=List[int])
+        output = comp.run(input_0=[1, 2], input_1=[3, 4])
+        assert output == {"output": [1, 2, 3, 4]}
+
+    @pytest.mark.unit
+    def test_join_str(self):
+        comp = Join(inputs_count=2, inputs_type=str)
+        output = comp.run(input_0="hello", input_1="test")
+        assert output == {"output": "hellotest"}
+
+    @pytest.mark.unit
+    def test_join_one_input(self):
+        comp = Join(inputs_count=1, inputs_type=str)
+        output = comp.run(input_0="hello")
+        assert output == {"output": "hello"}
+
+    @pytest.mark.unit
+    def test_join_zero_input(self):
+        with pytest.raises(ValueError):
+            Join(inputs_count=0, inputs_type=str)

test/preview/utils/test_marshalling.py

@@ -0,0 +1,37 @@
+import pytest
+
+from haystack.preview import Document, DeserializationError
+from haystack.preview.utils.marshalling import marshal_type, unmarshal_type
+
+
+TYPE_STRING_PAIRS = [(int, "int"), (Document, "haystack.preview.dataclasses.document.Document")]
+
+
+@pytest.mark.unit
+@pytest.mark.parametrize("type_,string", TYPE_STRING_PAIRS)
+def test_marshal_type(type_, string):
+    assert marshal_type(type_) == string
+
+
+@pytest.mark.unit
+@pytest.mark.parametrize("type_,string", TYPE_STRING_PAIRS)
+def test_unmarshal_type(type_, string):
+    assert unmarshal_type(string) == type_
+
+
+@pytest.mark.unit
+def test_unmarshal_type_missing_builtin():
+    with pytest.raises(DeserializationError, match="Could not locate builtin called 'something'"):
+        unmarshal_type("something")
+
+
+@pytest.mark.unit
+def test_unmarshal_type_missing_module():
+    with pytest.raises(DeserializationError, match="Could not locate the module 'something'"):
+        unmarshal_type("something.int")
+
+
+@pytest.mark.unit
+def test_unmarshal_type_missing_type():
+    with pytest.raises(DeserializationError, match="Could not locate the type 'Documentttt'"):
+        unmarshal_type("haystack.preview.dataclasses.document.Documentttt")