Add delete_bins to C API

examples/cpp/advanced-filling.cpp

@@ -173,6 +173,37 @@ int main() {
 
     pineappl_grid_write(grid, "advanced-filling.pineappl.lz4");
 
+    //-----------------------------------------------------------------------//
+
+    // Remove the bins for which the convolution is zero.
+    std::vector<uintptr_t> zero_indices;
+    zero_indices.reserve(dxsec.size());
+    for (size_t i = 0; i < dxsec.size(); ++i) {
+        if (dxsec[i] == 0.0) {
+           zero_indices.push_back(static_cast<uintptr_t>(i));
+        }
+    }
+    pineappl_grid_delete_bins(grid, zero_indices.data(), zero_indices.size());
+
+    std::vector<double> dxsec_no_zeros(pineappl_grid_bin_count(grid));
+    pineappl_grid_convolve(grid, xfx, alphas, pdf_states, pdf.get(), order_mask, channel_mask,
+        nullptr, 1, mmu_scales.data(), dxsec_no_zeros.data());
+
+    // Print table header
+    std::cout << " " << std::endl;
+    std::cout << std::setw(10) << "bin left"
+              << std::setw(12) << "bin right"
+              << std::setw(15) << "dsig/dx" << std::endl;
+    std::cout << std::string(37, '-') << std::endl;
+
+    // Loop through bins and print results
+    for (size_t i = 0; i < dxsec_no_zeros.size(); ++i) {
+        std::cout << std::setw(10) << bins[i]
+                  << std::setw(12) << bins[i + 1]
+                  << std::setw(15) << std::scientific << std::setprecision(3) << dxsec_no_zeros[i]
+                  << std::endl;
+    }
+
     // release memory
     pineappl_grid_delete(grid);
 }

examples/cpp/advanced-filling.output

@@ -24,3 +24,7 @@
  2.100e+00   2.200e+00      0.000e+00
  2.200e+00   2.300e+00      0.000e+00
  2.300e+00   2.400e+00      0.000e+00
+
+  bin left   bin right        dsig/dx
+-------------------------------------
+ 0.000e+00   1.000e-01      6.683e+03

pineappl_capi/src/lib.rs

@@ -860,6 +860,29 @@ pub unsafe extern "C" fn pineappl_grid_merge_bins(grid: *mut Grid, from: usize,
     grid.merge_bins(from..to).unwrap();
 }
 
+/// Deletes bins with the corresponding `bin_indices`. Repeated indices and indices larger or
+/// equal the bin length are ignored.
+///
+/// # Safety
+///
+///  The parameter `grid` must be valid `Grid` object created by either `pineappl_grid_new` or
+///  `pineappl_grid_read`.
+///  The parameter `bin_indices_ptr` must be an array of size `bin_indices_len`.
+///
+/// # Panics
+///
+/// TODO
+#[no_mangle]
+pub unsafe extern "C" fn pineappl_grid_delete_bins(
+    grid: *mut Grid,
+    bin_indices_ptr: *const usize,
+    bin_indices_len: usize,
+) {
+    let grid = unsafe { &mut *grid };
+    let bin_indices = unsafe { std::slice::from_raw_parts(bin_indices_ptr, bin_indices_len) };
+    grid.delete_bins(bin_indices);
+}
+
 /// Merges `other` into `grid` and subsequently deletes `other`.
 ///
 /// # Safety