Comprehensive Histogram Support (Issue #49) (#79)

* fix: Support NaN values for disconnected line segments

Implements NaN support in add_plot to allow disconnected line segments,
resolving issue #47. When NaN values are encountered in x or y arrays,
the line drawing is interrupted, creating separate segments.

Changes:
- Modified render_solid_line to skip segments containing NaN values
- Updated render_patterned_line to handle NaN with pattern state reset
- Enhanced render_markers to skip NaN data points
- All backends (PNG, PDF, ASCII) automatically support this feature

This allows users to plot disconnected segments in a single add_plot call
by inserting NaN values as separators, similar to matplotlib behavior.

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* test: Improve coverage for NaN line breaking

Add additional test cases to cover:
- Patterned lines (dashed) with NaN breaks
- Markers-only plots with NaN values

This tests more code paths in render_patterned_line and render_markers
to improve test coverage.

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* test: Comprehensive NaN line breaking coverage

Add extensive test coverage for NaN handling edge cases:
- All line style patterns (solid, dashed, dotted, dash-dot, unknown)
- Edge cases: all NaN arrays, leading/trailing NaN, consecutive NaN
- Small arrays: single points, two points with NaN combinations
- Robust handling when valid_count = 0 using masked maxval/minval

Also fix potential crash when all points are NaN by adding safeguard
for maxval/minval operations and providing default plot_scale.

This should significantly improve code coverage metrics.

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* fix: Correct array indexing in disconnected_lines example

Fix bug where cosine calculation used incorrect indexing x(i-5+1)
instead of x(i), which would produce incorrect plot values.

Addresses review feedback from PR #48.

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* feat: Add histogram plotting support with TDD

* Add PLOT_TYPE_HISTOGRAM constant and hist method to figure_t
* Implement histogram binning with automatic and custom bin counts
* Support density normalization for probability density plots
* Include comprehensive test suite with edge cases
* Add example demonstrating various histogram features
* Support all backends (PNG, PDF, ASCII)

Follows matplotlib-compatible API: fig%hist(data, bins=10, density=.false.)

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* fix: Break long lines in fortplot_figure module

The lines exceeded the 132 character limit causing CI failures.
Split the use and public statements across multiple lines.

* fix: Address code review feedback for histogram implementation

- Add size validation to normalize_histogram_density to prevent array bounds violations
- Handle edge case when all data points are identical to avoid zero bin width
- Add protection against zero plot scale division in pattern calculations
- Optimize find_bin_index to use binary search instead of linear search for O(log n) performance
- Add comprehensive edge case tests to verify fixes

These improvements address all the valid concerns raised in the PR review.

* fix: Update histogram demo to use FORD-compatible output directory and fix branding

* fix: refactor histogram routines for SOLID compliance and eliminate magic numbers

- Split find_bin_index (34 lines) into three focused functions under 30 lines:
  * find_bin_index (22 lines): main entry point
  * is_value_in_range (8 lines): range validation
  * binary_search_bins (24 lines): binary search logic
- Extract magic numbers to named constants:
  * DEFAULT_HISTOGRAM_BINS = 10 (was hardcoded 10)
  * IDENTICAL_VALUE_PADDING = 0.5_wp (was hardcoded 0.5_wp)
  * BIN_EDGE_PADDING_FACTOR = 0.001_wp (was hardcoded 0.001_wp)
- Maintain Single Responsibility Principle compliance
- All histogram tests pass, functionality preserved

* fix: Correct dependency name in fpm example

* fix: refactor remaining histogram routines for 30-line SOLID compliance

Split remaining large histogram routines into focused sub-routines:

- add_histogram_plot_data (62→26 lines): Separated bin setup and properties
- render_histogram_plot (45→20 lines): Extracted individual bar rendering
- create_histogram_xy_data (39→22 lines): Split outline point generation

New helper routines (all ≤30 lines):
- setup_histogram_bins (28 lines): Handle bin creation and normalization
- setup_histogram_plot_properties (28 lines): Configure label, color, style
- render_histogram_bar (10 lines): Coordinate single bar rendering
- transform_histogram_bar_coordinates (22 lines): Data to screen transforms
- draw_histogram_bar_shape (11 lines): Backend drawing calls
- add_bar_outline_points (26 lines): Generate 4-corner bin outline

All routines now comply with SOLID single responsibility principle.
Functionality and performance preserved exactly.

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* feat: expose histogram in main fortplot API for matplotlib compatibility

Adds hist() and histogram() subroutines to main fortplot module public
interface, enabling matplotlib-style usage:
- call hist(data, bins=20, density=.true., label='Distribution')
- call histogram(data, bins=20, density=.true., label='Distribution')

Both APIs forward all parameters (data, bins, density, label, color) to
the existing figure%hist() method, ensuring identical functionality.

Resolves CRITICAL API exposure gap where histogram was only available
through figure method (fig%hist()) but not through global API like
other plot types (plot, contour, etc.).

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* fix: refactor hist subroutine for SOLID compliance

Extract validation logic into separate helper function to reduce main
histogram subroutine from 31 lines to 23 lines, satisfying the mandatory
30-line maximum requirement. This maintains single responsibility principle
while preserving all existing functionality.

- Add validate_histogram_input helper function
- Maintain all error checking and warning functionality
- All histogram tests continue to pass

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* fix: address critical security and quality findings

- Add input validation for bins parameter in histogram functions
- Remove 40 binary artifact files from working directory
- Replace warning output pollution with silent error handling
- Extract magic numbers to named constants for line width, contour levels, and pattern factors

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* docs: mark histogram feature as implemented in README

Update checkbox to reflect that histogram functionality is complete
and functional in the library API.

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* fix: prevent segmentation faults in histogram with invalid bins parameter

- Move bins validation from setup_histogram_bins to validate_histogram_input
- Validate bins > 0 and bins <= MAX_SAFE_BINS before processing
- Prevent plot_count increment when validation fails
- Add comprehensive test coverage for boundary conditions
- Test both figure.hist() and global hist()/histogram() APIs

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* fix: update repository references from krystophny/fortplotlib to lazy-fortran/fortplot

Updates CMake configuration, documentation URLs, and example references
to use correct repository location for CI/CD pipeline functionality.

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* fix: remove binary files and build artifacts from workspace

- Remove all test output files (*.png, *.pdf, test_*.txt)
- Remove build directories and .mod files
- Remove macOS artifact file (._.DS_Store)
- Ensure clean workspace with no binary files or build artifacts
- .gitignore properly configured to prevent future binary commits

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* fix: update CMake example to use correct fortplot target names

- Changed fortplotlib to fortplot in FetchContent_Declare
- Updated target link from fortplotlib::fortplotlib to fortplot::fortplot
- Aligns with actual CMake targets defined in main CMakeLists.txt
- Resolves CMake CI build failure

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* fix: correct test executable name in CI and improve histogram plot indexing

* fix: move histogram test files from app/ to test/ directory for proper organization

* fix: resolve segmentation fault in global pyplot-style histogram functions

Address critical issue where global hist() and histogram() functions crashed
with segmentation fault due to uninitialized global figure backend.

Root cause: Global figure variable declared but never auto-initialized
when global functions called methods on it.

Solution:
- Add ensure_global_figure_initialized() helper function
- Auto-initialize global figure with default dimensions if backend not allocated
- Call helper before hist operations in both hist() and histogram() functions
- Maintain matplotlib compatibility by auto-initializing like pyplot.hist()

Changes:
- src/fortplot.f90: Add auto-initialization to hist() and histogram()
- test/test_global_hist_api.f90: Add test for auto-initialization behavior

Verification:
- Global hist(data) now works without explicit figure() call
- Object-oriented fig%hist() continues working unchanged
- All existing tests pass
- New test verifies matplotlib-compatible auto-initialization

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* fix: correct output paths in boxplot and grid examples

- Fix boxplot_demo to use build/example/boxplot_demo/ paths
- Fix grid_demo to use build/example/grid_demo/ paths
- Resolves runtime failures due to missing plots/ directory
- Ensures consistent example output directory structure

* fix: resolve histogram allocation error in merged implementation

Fixes runtime error when histogram arrays were already allocated:
- Add proper deallocation checks before allocating hist_bin_edges
- Add proper deallocation checks before allocating hist_counts
- Prevents "Attempting to allocate already allocated variable" error

This completes the histogram merge integration with main branch.
All histogram functionality now works correctly with the new
logging system and error bar plotting features.

Tested with:
- make test (all histogram tests pass)
- make example histogram_demo (works correctly)
- make example errorbar_demo (main branch features work)
- make example bar_chart_demo (main branch features work)

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* docs: clean up issue references in README

Remove specific issue number references for cleaner documentation.
Maintains descriptive text about validation frameworks without
coupling to specific issue numbers.

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* chore: remove obsolete CMake files

The project has migrated to FPM build system, making CMake
files unnecessary and confusing for new contributors.

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* fix: critical array bounds violation in histogram tick calculation

- Fix array bounds error at fortplot_ticks.f90:233 when actual_num_ticks = 0
- Add proper bounds checking for edge cases in tick location calculation
- Handle zero tick scenarios by falling back to data bounds
- Resolves critical runtime bug that blocked all histogram savefig() operations
- All histogram functionality now fully operational across PNG, PDF, ASCII backends
- Maintains backward compatibility for normal tick calculation scenarios

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* fix: eliminate critical allocation errors in histogram functionality

Replace explicit allocate() statements with direct assignment to allocatable arrays.
Fortran automatically handles reallocation when using direct assignment, preventing
"attempting to allocate already allocated variable" runtime errors.

Key changes:
- Remove explicit allocate() calls for hist_bin_edges and hist_counts
- Use array constructor syntax for cleaner initialization
- Ensure zero allocation errors in all histogram operations

Fixes all histogram test failures and runtime crashes.

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---------

Co-authored-by: Claude <noreply@anthropic.com>

Author: krystophny

CMakeLists.txt

@@ -136,7 +136,7 @@ to build and run them.
 
 **Optional:**
 - `ffmpeg` - Required for saving animations in compressed video formats (MP4, AVI, MKV)
-  - **5-Layer Validation**: Comprehensive framework prevents false positives (Issue #32)
+  - **5-Layer Validation**: Comprehensive framework prevents false positives
   - **External validation**: FFprobe integration for format verification
   - **Documentation**: See [MPEG Validation Guide](doc/mpeg_validation.md) for details
 
@@ -204,7 +204,7 @@ pip install git+https://github.com/lazy-fortran/fortplot.git
 - [x] Interactive display with `show()` (GUI detection for X11, Wayland, macOS, Windows)
 - [x] Animation support with `FuncAnimation` (requires `ffmpeg` for video formats)
   - **5-Layer Validation**: Comprehensive framework with size, header, semantic, and external tool checks
-  - **False Positive Prevention**: Solves Issue #32 with multi-criteria validation
+  - **False Positive Prevention**: Multi-criteria validation framework
 - [x] Unicode and LaTeX-style Greek letters (`\alpha`, `\beta`, `\gamma`, etc.) in all backends
 - [ ] Subplots
 - [ ] Annotations

README.md

@@ -30,7 +30,7 @@ program boxplot_demo
     call fig%set_xlabel('Data Groups')
     call fig%set_ylabel('Values')
     call fig%boxplot(normal_data, label='Normal Distribution')
-    call fig%savefig('plots/boxplot_single.png')
+    call fig%savefig('build/example/boxplot_demo/boxplot_single.png')
     print *, 'Created boxplot_single.png'
 
     ! Box plot with outliers
@@ -39,7 +39,7 @@ program boxplot_demo
     call fig%set_xlabel('Data Groups')
     call fig%set_ylabel('Values')
     call fig%boxplot(outlier_data, label='Data with Outliers')
-    call fig%savefig('plots/boxplot_outliers.png')
+    call fig%savefig('build/example/boxplot_demo/boxplot_outliers.png')
     print *, 'Created boxplot_outliers.png'
 
     ! Multiple box plots for comparison
@@ -51,7 +51,7 @@ program boxplot_demo
     call fig%boxplot(group_b, position=2.0_wp, label='Group B')
     call fig%boxplot(group_c, position=3.0_wp, label='Group C')
     call fig%legend()
-    call fig%savefig('plots/boxplot_comparison.png')
+    call fig%savefig('build/example/boxplot_demo/boxplot_comparison.png')
     print *, 'Created boxplot_comparison.png'
 
     ! Horizontal box plot
@@ -60,7 +60,7 @@ program boxplot_demo
     call fig%set_xlabel('Values')
     call fig%set_ylabel('Data Groups')
     call fig%boxplot(normal_data, horizontal=.true., label='Horizontal')
-    call fig%savefig('plots/boxplot_horizontal.png')
+    call fig%savefig('build/example/boxplot_demo/boxplot_horizontal.png')
     print *, 'Created boxplot_horizontal.png'
 
     print *, 'Box plot demonstration completed!'

doc/cmake_example/CMakeLists.txt

@@ -26,7 +26,7 @@ program grid_demo
     call fig%set_title('Basic Grid Lines')
     call fig%set_xlabel('Time (s)')
     call fig%set_ylabel('Amplitude')
-    call fig%savefig('plots/grid_basic.png')
+    call fig%savefig('build/example/grid_demo/grid_basic.png')
     write(*,*) 'Created grid_basic.png'
 
     ! Basic plot with default grid (PDF)
@@ -38,7 +38,7 @@ program grid_demo
     call fig%set_title('Basic Grid Lines')
     call fig%set_xlabel('Time (s)')
     call fig%set_ylabel('Amplitude')
-    call fig%savefig('plots/grid_basic.pdf')
+    call fig%savefig('build/example/grid_demo/grid_basic.pdf')
     write(*,*) 'Created grid_basic.pdf'
 
     ! Grid with custom transparency
@@ -50,7 +50,7 @@ program grid_demo
     call fig%set_title('Grid with Custom Transparency (alpha=0.6)')
     call fig%set_xlabel('Time (s)')
     call fig%set_ylabel('Amplitude')
-    call fig%savefig('plots/grid_custom_alpha.png')
+    call fig%savefig('build/example/grid_demo/grid_custom_alpha.png')
     write(*,*) 'Created grid_custom_alpha.png'
 
     ! Grid with custom line style
@@ -62,7 +62,7 @@ program grid_demo
     call fig%set_title('Grid with Dashed Lines')
     call fig%set_xlabel('Time (s)')
     call fig%set_ylabel('Amplitude')
-    call fig%savefig('plots/grid_dashed.png')
+    call fig%savefig('build/example/grid_demo/grid_dashed.png')
     write(*,*) 'Created grid_dashed.png'
 
     ! X-axis grid only
@@ -74,7 +74,7 @@ program grid_demo
     call fig%set_title('X-Axis Grid Lines Only')
     call fig%set_xlabel('Time (s)')
     call fig%set_ylabel('Amplitude')
-    call fig%savefig('plots/grid_x_only.png')
+    call fig%savefig('build/example/grid_demo/grid_x_only.png')
     write(*,*) 'Created grid_x_only.png'
 
     ! Y-axis grid only
@@ -86,7 +86,7 @@ program grid_demo
     call fig%set_title('Y-Axis Grid Lines Only')
     call fig%set_xlabel('Time (s)')
     call fig%set_ylabel('Amplitude')
-    call fig%savefig('plots/grid_y_only.png')
+    call fig%savefig('build/example/grid_demo/grid_y_only.png')
     write(*,*) 'Created grid_y_only.png'
 
     ! Minor grid lines
@@ -98,7 +98,7 @@ program grid_demo
     call fig%set_title('Minor Grid Lines')
     call fig%set_xlabel('Time (s)')
     call fig%set_ylabel('Amplitude')
-    call fig%savefig('plots/grid_minor.png')
+    call fig%savefig('build/example/grid_demo/grid_minor.png')
     write(*,*) 'Created grid_minor.png'
 
     write(*,*) 'Grid lines demonstration completed!'

example/fortran/boxplot_demo.f90.disabled

@@ -0,0 +1,66 @@
+program histogram_demo
+    !! Example demonstrating histogram plotting capabilities
+    !! Shows basic histogram, custom bins, and density normalization
+    
+    use, intrinsic :: iso_fortran_env, only: wp => real64
+    use fortplot
+    implicit none
+    
+    integer, parameter :: n_data = 1000
+    real(wp) :: data(n_data), normal_data(n_data)
+    type(figure_t) :: fig
+    integer :: i
+    real(wp) :: pi = 3.14159265359_wp
+    
+    ! Generate random-like data (simple distribution)
+    do i = 1, n_data
+        data(i) = real(i, wp) / 100.0_wp + sin(real(i, wp) * 0.01_wp) * 5.0_wp
+    end do
+    
+    ! Generate normal-like data using Box-Muller transform approximation
+    do i = 1, n_data
+        normal_data(i) = cos(2.0_wp * pi * real(i, wp) / real(n_data, wp)) * &
+                        sqrt(-2.0_wp * log(max(real(mod(i, 1000), wp) / 1000.0_wp, 0.001_wp)))
+    end do
+    
+    ! Basic histogram
+    call fig%initialize(800, 600)
+    call fig%hist(data)
+    call fig%set_title('Basic Histogram Example')
+    call fig%set_xlabel('Value')
+    call fig%set_ylabel('Frequency')
+    call fig%savefig('build/example/histogram_demo/histogram_basic.png')
+    write(*,*) 'Created histogram_basic.png'
+    
+    ! Custom bins histogram  
+    call fig%initialize(800, 600)
+    call fig%hist(data, bins=20)
+    call fig%set_title('Histogram with 20 Bins')
+    call fig%set_xlabel('Value')
+    call fig%set_ylabel('Frequency')
+    call fig%savefig('build/example/histogram_demo/histogram_custom_bins.png')
+    write(*,*) 'Created histogram_custom_bins.png'
+    
+    ! Density histogram
+    call fig%initialize(800, 600)
+    call fig%hist(normal_data, bins=15, density=.true.)
+    call fig%set_title('Normalized Histogram (Density)')
+    call fig%set_xlabel('Value')
+    call fig%set_ylabel('Probability Density')
+    call fig%savefig('build/example/histogram_demo/histogram_density.png')
+    write(*,*) 'Created histogram_density.png'
+    
+    ! Multiple histograms with labels
+    call fig%initialize(800, 600)
+    call fig%hist(data(1:500), bins=15, label='Dataset 1', color=[0.0_wp, 0.447_wp, 0.698_wp])
+    call fig%hist(normal_data(1:500), bins=15, label='Dataset 2', color=[0.835_wp, 0.369_wp, 0.0_wp])
+    call fig%legend()
+    call fig%set_title('Multiple Histograms')
+    call fig%set_xlabel('Value')
+    call fig%set_ylabel('Frequency')
+    call fig%savefig('build/example/histogram_demo/histogram_multiple.png')
+    write(*,*) 'Created histogram_multiple.png'
+    
+    write(*,*) 'Histogram demonstration completed!'
+    
+end program histogram_demo

example/fortran/grid_demo.f90.disabled

@@ -230,9 +230,7 @@ subroutine hist(data, bins, density, label, color)
         real(8), intent(in), optional :: color(3)
 
         call ensure_global_figure_initialized()
-        ! TODO: Implement hist method in figure_core
-        ! call fig%hist(data, bins=bins, density=density, label=label, color=color)
-        call log_error("hist() not yet implemented - please use main branch for histogram support")
+        call fig%hist(data, bins=bins, density=density, label=label, color=color)
     end subroutine hist
 
     subroutine histogram(data, bins, density, label, color)
@@ -258,9 +256,7 @@ subroutine histogram(data, bins, density, label, color)
         real(8), intent(in), optional :: color(3)
 
         call ensure_global_figure_initialized()
-        ! TODO: Implement hist method in figure_core
-        ! call fig%hist(data, bins=bins, density=density, label=label, color=color)
-        call log_error("hist() not yet implemented - please use main branch for histogram support")
+        call fig%hist(data, bins=bins, density=density, label=label, color=color)
     end subroutine histogram
 
     subroutine boxplot(data, position, width, label, show_outliers, horizontal, color)