Support block in CSV::Row#to_h by tsymbalenkovlad · Pull Request #356 · ruby/csv

tsymbalenkovlad · 2026-04-29T07:59:35Z

It will be consistent with Ruby's method, otherwise it has to be like row.entries.to_h { ... }

kou · 2026-04-30T08:55:56Z

+        new_key, new_value = if block_given?
+          yield(key, value)
+        else
+          [key, value]


Thanks, that's a good one

kou · 2026-04-30T08:57:13Z

+    row2 =  CSV::Row.new(%w{A B C}, [1, 2, 3])
+    hash2 = row2.to_hash { |k, v| [k, v ** 2] }
+    assert_equal({"A" => 1, "B" => 4, "C" => 9}, hash2)


Could you create a separated test?

kou · 2026-04-30T10:05:11Z

+      each do |key, value|
+        key, value = yield(key, value) if block_given?


Ah, sorry. We need to call self[key]:

Suggested change

each do |key, value|

key, value = yield(key, value) if block_given?

each do |key, _value|

value = self[key]

key, value = yield(key, value) if block_given?

Co-authored-by: Sutou Kouhei <kou@cozmixng.org>

Copilot

Pull request overview

Adds support for passing a block to CSV::Row#to_h / #to_hash, aligning usage with Ruby’s to_h { ... } pattern and avoiding the need for row.entries.to_h { ... }.

Changes:

Add a new test covering CSV::Row#to_hash with a block.
Update CSV::Row#to_h to yield each key/value pair to an optional block before insertion.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

File	Description
test/csv/test_row.rb	Adds a test for block form of `to_hash`.
lib/csv/row.rb	Implements yielding to an optional block in `to_h` during hash construction.

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      each do |key, _value|
-        hash[key] = self[key] unless hash.key?(key)
+        value = self[key]
+        key, value = yield(key, value) if block_given?
+
+        hash[key] = value unless hash.key?(key)


      each do |key, _value|
-        hash[key] = self[key] unless hash.key?(key)
+        value = self[key]
+        key, value = yield(key, value) if block_given?


    def to_h
      hash = {}
      each do |key, _value|
-        hash[key] = self[key] unless hash.key?(key)
+        value = self[key]
+        key, value = yield(key, value) if block_given?
+
+        hash[key] = value unless hash.key?(key)


+    row = CSV::Row.new(%w{A B C}, [1, 2, 3])
+    hash = row.to_hash { |k, v| [k, v ** 2] }


    def to_h
      hash = {}
      each do |key, _value|
-        hash[key] = self[key] unless hash.key?(key)
+        value = self[key]
+        key, value = yield(key, value) if block_given?


kou · 2026-04-30T20:48:40Z

      hash = {}
      each do |key, _value|
-        hash[key] = self[key] unless hash.key?(key)
+        next if hash.key?(key)


key may be changed by yield(key, value). So we can't do this if block_given?.

How about using separated each?

if block_given? each do |key, _value| key, value = yield(key, self[key]) hash[key] = value unless hash.key?(key) end else each do |key, _value| hash[key] = self[key] unless hash.key?(key) end end

Copilot

Pull request overview

Adds block support to CSV::Row#to_h (and therefore #to_hash) to align with Ruby’s to_h { ... } conversion pattern, so callers don’t need to go through row.entries.to_h { ... }.

Changes:

Extend CSV::Row#to_h to accept an optional block that transforms each (key, value) pair before insertion.
Document the new block form in CSV::Row#to_h’s RDoc.
Add a unit test exercising to_hash with a block.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
test/csv/test_row.rb	Adds coverage for `CSV::Row#to_hash` accepting a block.
lib/csv/row.rb	Implements and documents block support for `CSV::Row#to_h`/`#to_hash`.

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      each do |key, _value|
-        hash[key] = self[key] unless hash.key?(key)
+        next if hash.key?(key)
+
+        value = self[key]
+        key, value = yield(key, value) if block_given?
+
+        hash[key] = value


+        next if hash.key?(key)
+
+        value = self[key]
+        key, value = yield(key, value) if block_given?


+    row = CSV::Row.new(%w{A A B C}, [1, 2, 2, 3])
+    hash = row.to_hash { |k, v| [k, v**2] }
+    assert_equal({"A" => 1, "B" => 4, "C" => 9}, hash)


Copilot

Pull request overview

This PR adds support for passing a block to CSV::Row#to_h/#to_hash, aligning the API shape with Ruby’s to_h { ... } usage while keeping CSV::Row#to_h as the primary conversion entrypoint.

Changes:

Add a new test covering CSV::Row#to_hash with a block and basic error cases for invalid block return values.
Extend CSV::Row#to_h to accept an optional block and transform (key, value) pairs via the block result.
Update the to_h method documentation to include the block form and an example.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
`test/csv/test_row.rb`	Adds coverage for `to_hash` when a block is provided, including error handling expectations.
`lib/csv/row.rb`	Implements block support in `CSV::Row#to_h` and updates the method docs accordingly.

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+          raise TypeError, "wrong element type #{result.class} (expected array)" unless result.is_a?(Array)
+          raise ArgumentError, "wrong array length (expected 2, was #{result.size})" unless result.size == 2
+
+          key, value = result


+      if block_given?
+        each do |key, _value|
+          result = yield(key, self[key])
+          raise TypeError, "wrong element type #{result.class} (expected array)" unless result.is_a?(Array)
+          raise ArgumentError, "wrong array length (expected 2, was #{result.size})" unless result.size == 2
+
+          key, value = result
+          hash[key] = value unless hash.key?(key)
+        end


+    new_keys_map = {"A" => "A", "B" => "B", "C" => "B"}
+    hash = row.to_hash { |k, v| [new_keys_map[k], v**2] }
+    assert_equal({"A" => 1, "B" => 4}, hash)
+    hash.keys.each_with_index do |string_key, h|


+          raise TypeError, "wrong element type #{result.class} (expected array)" unless result.is_a?(Array)
+          raise ArgumentError, "wrong array length (expected 2, was #{result.size})" unless result.size == 2
+
+          key, value = result


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Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

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+    #   source = "Name,Value\nfoo,1\nbar,2\nbaz,3\n"
+    #   table = CSV.parse(source, headers: true)
+    #   row = table[0]
+    #   row.to_h { |key, value| [key, value.to_i * 2] } # => {"Name"=>"foo", "Value"=>2}


+          result = Array.try_convert(yield(key, self[key]))
+          raise TypeError, "wrong element type #{result.class} (expected array)" if result.nil?
+          raise ArgumentError, "wrong array length (expected 2, was #{result.size})" unless result.size == 2
+
+          key, value = result


+
+      if block_given?
+        each do |key, _value|
+          result = Array.try_convert(yield(key, self[key]))


+        each do |key, _value|
+          hash[key] = self[key] unless hash.key?(key)
+        end


+  def test_to_hash_with_block
+    row = CSV::Row.new(%w{A A B C}, [1, 2, 2, 3])
+    new_keys_map = {"A" => "A", "B" => "B", "C" => "B"}
+    hash = row.to_hash { |k, v| [new_keys_map[k], v**2] }
+    assert_equal({"A" => 1, "B" => 4}, hash)


kou · 2026-05-01T21:20:48Z

+          key.freeze if key.is_a?(String) && !key.frozen?
+          hash[key] = value unless hash.key?(key)


Could you avoid needless freeze check?

Suggested change

key.freeze if key.is_a?(String) && !key.frozen?

hash[key] = value unless hash.key?(key)

next if hash.key?(key)

key.freeze if key.is_a?(String) && !key.frozen?

hash[key] = value

@tsymbalenkovlad What do you think about this?

Oh sorry I didn't see code suggestion and thought it's about removing !key.frozen?

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Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

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+      if block_given?
+        each do |key, _value|
+          result = yield(key, self[key])
+          result_array = Array.try_convert(result)
+          raise TypeError, "wrong element type #{result.class} (expected array)" if result_array.nil?
+          raise ArgumentError, "wrong array length (expected 2, was #{result_array.size})" unless result_array.size == 2
+
+          key, value = result_array
+          key.freeze if key.is_a?(String)
+          hash[key] = value unless hash.key?(key)
+        end


+  def test_to_hash_with_block
+    row = CSV::Row.new(%w{A A B C}, [1, 2, 2, 3])
+    new_keys_map = {"A" => "A", "B" => "B", "C" => "B"}
+    hash = row.to_hash { |k, v| [new_keys_map[k], v**2] }
+    assert_equal({"A" => 1, "B" => 4}, hash)
+    hash.each_key do |string_key|
+      assert_predicate(string_key, :frozen?)
+    end
+
+    assert_raise TypeError do
+      row.to_hash { "foo" }
+    end
+
+    assert_raise ArgumentError do
+      row.to_hash { [1] }
+    end
+  end


kou · 2026-05-02T21:45:20Z

    new_keys_map = {"A" => "A", "B" => "B", "C" => "B"}
-    hash = row.to_hash { |k, v| [new_keys_map[k], v**2] }
-    assert_equal({"A" => 1, "B" => 4}, hash)
-    hash.each_key do |string_key|
+    hash2 = row.to_hash { |k, v| [new_keys_map[k], v**2] }
+    assert_equal({"A" => 1, "B" => 4}, hash2)
+    hash2.each_key do |string_key|
      assert_predicate(string_key, :frozen?)
    end


Could you split this duplicated key case to a separated test?

We can merge this after it.

kou · 2026-05-02T21:47:01Z

+          key.freeze if key.is_a?(String) && !key.frozen?
+          hash[key] = value unless hash.key?(key)


…tions only

kou · 2026-05-03T22:07:51Z

Thanks.

Do you want to use this feature soon? (Should we release a new version soon?)

tsymbalenkovlad · 2026-05-04T06:31:21Z

@kou No rush, I have a patch in project

Thanks

Support block in CSV::Row#to_h

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kou reviewed Apr 30, 2026

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tsymbalenkovlad added 2 commits April 30, 2026 12:35

Simplify block_given? case based on @kou feedback

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Separate block test case

a11c20f

tsymbalenkovlad requested a review from kou April 30, 2026 09:37

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Get value from self

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Comment thread test/csv/test_row.rb Outdated

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Fix formatting

8257d8e

Co-authored-by: Sutou Kouhei <kou@cozmixng.org>

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tsymbalenkovlad added 2 commits April 30, 2026 14:59

Improve condition and test, add documentation

a01ef69

Merge branch 'main' of github.com:tsymbalenkovlad/csv

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tsymbalenkovlad added 6 commits May 3, 2026 09:45

Add call-seq doc

1298ed9

Handle repeated headers in block, validate block result type

f1bbb99

Improve validation of block result

ff84e8a

Fix class in error and doc

a8797a1

Skip duplicate transformed key earlier, add spec for value transforma…

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…tions only

Separate tests

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kou merged commit 4a5c504 into ruby:main May 3, 2026
60 of 68 checks passed

		each do \|key, value\|
		key, value = yield(key, value) if block_given?

		row = CSV::Row.new(%w{A B C}, [1, 2, 3])
		hash = row.to_hash { \|k, v\| [k, v ** 2] }

		key.freeze if key.is_a?(String) && !key.frozen?
		hash[key] = value unless hash.key?(key)

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tsymbalenkovlad commented Apr 29, 2026

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