[REVIEW] Remove string_view is_null method

CHANGELOG.md

@@ -16,6 +16,7 @@
 - PR #4073 Enable contiguous split java test
 - PR #4527 Add JNI and java bindings for matches_re
 - PR #4599 Add Java and JNI bindings for string replace
+- PR #4548 Remove string_view is_null method
 - PR #4645 Add Alias for `kurtosis` as `kurt`
 
 ## Bug Fixes

cpp/include/cudf/scalar/scalar.hpp

@@ -304,9 +304,7 @@ class string_scalar : public scalar {
    * 
    * @param stream The CUDA stream to do the operation in
    */
-  value_type value(cudaStream_t stream = 0) const {
-    return (is_valid(stream) && size()==0) ? value_type{"",0} : value_type{data(), size()};
-  }
+  value_type value(cudaStream_t stream = 0) const { return value_type{data(), size()}; }
 
   /**
    * @brief Returns the size of the string in bytes

cpp/include/cudf/scalar/scalar_device_view.cuh

@@ -158,10 +158,7 @@ class string_scalar_device_view
   /**
    * @brief Returns string_view of the value of this scalar.
    */
-  __device__ string_view value() const noexcept {
-    return (is_valid() && _size==0) ? string_view{"",0} :
-              string_view(this->data(), _size);
-  }
+  __device__ ValueType value() const noexcept { return ValueType{this->data(), _size}; }
 
   /**
    * @brief Returns a raw pointer to the value in device memory
@@ -170,6 +167,11 @@ class string_scalar_device_view
     return static_cast<char const*>(_data);
   }
 
+  /**
+   * @brief Returns the size of the string in bytes.
+   */
+  __device__ size_type size() const noexcept { return _size; }
+
  private:
   const char* _data{};  ///< Pointer to device memory containing the value
   size_type _size;      ///< Size of the string in bytes

cpp/include/cudf/strings/string_view.cuh

@@ -79,11 +79,6 @@ class string_view
    * @brief Return true if string has no characters
    */
   __host__ __device__ bool empty() const;
-  /**
-   * @brief Return true if string is NULL.
-   * That is, `data()==nullptr` for this instance.
-   */
-  __host__ __device__ bool is_null() const;
 
   /**
    * @brief Handy iterator for navigating through encoded characters.

cpp/include/cudf/strings/string_view.inl

@@ -97,11 +97,6 @@ __host__ __device__ inline bool string_view::empty() const
     return _bytes == 0;
 }
 
-__host__ __device__ inline bool string_view::is_null() const
-{
-    return _data == nullptr;
-}
-
 // this custom iterator knows about UTF8 encoding
 __device__ inline string_view::const_iterator::const_iterator(const string_view& str, size_type pos)
     : p{str.data()}, bytes{str.size_bytes()},
@@ -261,13 +256,9 @@ __device__ inline int string_view::compare(const string_view& in) const
 
 __device__ inline int string_view::compare(const char* data, size_type bytes) const
 {
+    size_type const len1 = size_bytes();
     const unsigned char* ptr1 = reinterpret_cast<const unsigned char*>(this->data());
-    if(!ptr1)
-        return -1;
     const unsigned char* ptr2 = reinterpret_cast<const unsigned char*>(data);
-    if(!ptr2)
-        return 1;
-    size_type len1 = size_bytes();
     size_type idx = 0;
     for(; (idx < len1) && (idx < bytes); ++idx)
     {

cpp/src/strings/combine.cu

@@ -16,6 +16,7 @@
 
 #include <cudf/column/column_factories.hpp>
 #include <cudf/column/column_device_view.cuh>
+#include <cudf/scalar/scalar_device_view.cuh>
 #include <cudf/strings/strings_column_view.hpp>
 #include <cudf/strings/string_view.cuh>
 #include <cudf/strings/combine.hpp>
@@ -58,11 +59,7 @@ std::unique_ptr<column> concatenate( table_view const& strings_columns,
 
     CUDF_EXPECTS( separator.is_valid(), "Parameter separator must be a valid string_scalar");
     string_view d_separator(separator.data(),separator.size());
-    string_view const d_narep = [&narep] {
-        if( !narep.is_valid() )
-            return string_view(nullptr,0);
-        return narep.size()==0 ? string_view("",0) : string_view(narep.data(),narep.size());
-    } ();
+    auto d_narep = get_scalar_device_view(const_cast<string_scalar&>(narep));
 
     // Create device views from the strings columns.
     auto table = table_device_view::create(strings_columns,stream);
@@ -75,7 +72,7 @@ std::unique_ptr<column> concatenate( table_view const& strings_columns,
         [d_table, d_narep] __device__ (size_type idx) {
             bool null_element = thrust::any_of( thrust::seq, d_table.begin(), d_table.end(),
                [idx] (auto col) { return col.is_null(idx);});
-            return( !null_element || !d_narep.is_null() );
+            return( !null_element || d_narep.is_valid() );
         }, stream, mr );
     rmm::device_buffer null_mask = valid_mask.first;
     auto null_count = valid_mask.second;
@@ -85,12 +82,12 @@ std::unique_ptr<column> concatenate( table_view const& strings_columns,
             // for this row (idx), iterate over each column and add up the bytes
             bool null_element = thrust::any_of( thrust::seq, d_table.begin(), d_table.end(),
                 [row_idx] (auto const& d_column) { return d_column.is_null(row_idx);});
-            if( null_element && d_narep.is_null() )
+            if( null_element && !d_narep.is_valid() )
                 return 0;
             size_type bytes = thrust::transform_reduce( thrust::seq, d_table.begin(), d_table.end(),
                 [row_idx, d_separator, d_narep] __device__ (column_device_view const& d_column) {
                     return d_separator.size_bytes() +
-                           (d_column.is_null(row_idx) ? d_narep.size_bytes()
+                           (d_column.is_null(row_idx) ? d_narep.size()
                                                       : d_column.element<string_view>(row_idx).size_bytes());
                 }, 0, thrust::plus<size_type>());
             // separator goes only in between elements
@@ -113,15 +110,15 @@ std::unique_ptr<column> concatenate( table_view const& strings_columns,
         [d_table, num_columns, d_separator, d_narep, d_results_offsets, d_results_chars] __device__(size_type idx){
             bool null_element = thrust::any_of( thrust::seq, d_table.begin(), d_table.end(),
                                                 [idx] (column_device_view const& col) { return col.is_null(idx);});
-            if( null_element && d_narep.is_null() )
+            if( null_element && !d_narep.is_valid() )
                 return; // do not write to buffer at all if any column element for this row is null
             size_type offset = d_results_offsets[idx];
             char* d_buffer = d_results_chars + offset;
             // write out each column's entry for this row
             for( size_type col_idx=0; col_idx < num_columns; ++col_idx )
             {
                 auto d_column = d_table.column(col_idx);
-                string_view d_str = d_column.is_null(idx) ? d_narep : d_column.element<string_view>(idx);
+                string_view d_str = d_column.is_null(idx) ? d_narep.value() : d_column.element<string_view>(idx);
                 d_buffer = detail::copy_string(d_buffer, d_str);
                 // separator goes only in between elements
                 if( col_idx+1 < num_columns )
@@ -148,11 +145,7 @@ std::unique_ptr<column> join_strings( strings_column_view const& strings,
 
     auto execpol = rmm::exec_policy(stream);
     string_view d_separator(separator.data(),separator.size());
-    string_view const d_narep = [&narep] {
-        if( !narep.is_valid() )
-            return string_view(nullptr,0);
-        return narep.size()==0 ? string_view("",0) : string_view(narep.data(),narep.size());
-    } ();
+    auto d_narep = get_scalar_device_view(const_cast<string_scalar&>(narep));
 
     auto strings_column = column_device_view::create(strings.parent(),stream);
     auto d_strings = *strings_column;
@@ -169,9 +162,9 @@ std::unique_ptr<column> join_strings( strings_column_view const& strings,
             size_type bytes = 0;
             if( d_strings.is_null(idx) )
             {
-                if( d_narep.is_null() )
+                if( !d_narep.is_valid() )
                     return 0; // skip nulls
-                bytes += d_narep.size_bytes();
+                bytes += d_narep.size();
             }
             else
                 bytes += d_strings.element<string_view>(idx).size_bytes();
@@ -197,7 +190,7 @@ std::unique_ptr<column> join_strings( strings_column_view const& strings,
     // only one entry so it is either all valid or all null
     size_type null_count = 0;
     rmm::device_buffer null_mask; // init to null null-mask
-    if( strings.null_count()==strings_count && d_narep.is_null() )
+    if( strings.null_count()==strings_count && !narep.is_valid() )
     {
         null_mask = create_null_mask(1,cudf::mask_state::ALL_NULL,stream,mr);
         null_count = 1;
@@ -211,9 +204,9 @@ std::unique_ptr<column> join_strings( strings_column_view const& strings,
             char* d_buffer = d_chars + offset;
             if( d_strings.is_null(idx) )
             {
-                if( d_narep.is_null() )
+                if( !d_narep.is_valid() )
                     return; // do not write to buffer if element is null (including separator)
-                d_buffer = detail::copy_string(d_buffer, d_narep);
+                d_buffer = detail::copy_string(d_buffer, d_narep.value());
             }
             else
             {

cpp/src/strings/filling/fill.cu

@@ -17,6 +17,7 @@
 #include <cudf/null_mask.hpp>
 #include <cudf/column/column_factories.hpp>
 #include <cudf/column/column_device_view.cuh>
+#include <cudf/scalar/scalar_device_view.cuh>
 #include <cudf/strings/strings_column_view.hpp>
 #include <cudf/strings/string_view.cuh>
 #include <cudf/strings/combine.hpp>
@@ -47,11 +48,7 @@ std::unique_ptr<column> fill( strings_column_view const& strings,
         return std::make_unique<column>( strings.parent() );
 
     // string_scalar.data() is null for valid, empty strings
-    string_view const d_value = [&] {
-        if( !value.is_valid() )
-            return string_view(nullptr,0);
-        return value.size()==0 ? string_view("",0) : string_view(value.data(),value.size());
-    } ();
+    auto d_value = get_scalar_device_view(const_cast<string_scalar&>(value));
 
     auto strings_column = column_device_view::create(strings.parent(),stream);
     auto d_strings = *strings_column;
@@ -61,19 +58,16 @@ std::unique_ptr<column> fill( strings_column_view const& strings,
         thrust::make_counting_iterator<size_type>(0),
         thrust::make_counting_iterator<size_type>(strings_count),
         [d_strings, begin, end, d_value] __device__ (size_type idx) {
-            return ((begin <= idx) && (idx < end)) ? !d_value.is_null() : !d_strings.is_null(idx);
+            return ((begin <= idx) && (idx < end)) ? d_value.is_valid() : !d_strings.is_null(idx);
         }, stream, mr );
     auto null_count = valid_mask.second;
     rmm::device_buffer& null_mask = valid_mask.first;
 
     // build offsets column
     auto offsets_transformer = [d_strings, begin, end, d_value] __device__ (size_type idx) {
-            if( ((begin <= idx) && (idx < end)) ? d_value.is_null() : d_strings.is_null(idx) )
+            if( ((begin <= idx) && (idx < end)) ? !d_value.is_valid() : d_strings.is_null(idx) )
                 return 0;
-            int32_t bytes = d_value.size_bytes();
-            if( (idx < begin) || (idx >= end) )
-                bytes = d_strings.element<string_view>(idx).size_bytes();
-            return bytes;
+            return ((begin <= idx) && (idx < end)) ? d_value.size() : d_strings.element<string_view>(idx).size_bytes();
         };
     auto offsets_transformer_itr = thrust::make_transform_iterator( thrust::make_counting_iterator<size_type>(0), offsets_transformer );
     auto offsets_column = detail::make_offsets_child_column(offsets_transformer_itr,
@@ -88,11 +82,10 @@ std::unique_ptr<column> fill( strings_column_view const& strings,
     auto d_chars = chars_column->mutable_view().data<char>();
     thrust::for_each_n(rmm::exec_policy(stream)->on(stream), thrust::make_counting_iterator<size_type>(0), strings_count,
         [d_strings, begin, end, d_value, d_offsets, d_chars] __device__(size_type idx){
-            if( ((begin <= idx) && (idx < end)) ? d_value.is_null() : d_strings.is_null(idx) )
+            if( ((begin <= idx) && (idx < end)) ? !d_value.is_valid() : d_strings.is_null(idx) )
                 return;
-            string_view d_str = d_value;
-            if( (idx < begin) || (idx >= end) )
-                d_str = d_strings.element<string_view>(idx);
+            string_view const d_str = ((begin <= idx) && (idx < end)) ? d_value.value() 
+                                      : d_strings.element<string_view>(idx);
             memcpy( d_chars + d_offsets[idx], d_str.data(), d_str.size_bytes() );
         });
 

cpp/src/strings/utilities.cu

@@ -99,8 +99,6 @@ std::unique_ptr<cudf::column> child_chars_from_string_vector(
     auto d_strings = strings.data().get();
     auto execpol = rmm::exec_policy(stream);
     size_type bytes = thrust::device_pointer_cast(d_offsets)[count];
-    if( (bytes==0) && (null_count < count) )
-        bytes = 1; // all entries are empty strings
 
     // create column
     auto chars_column = make_numeric_column( data_type{INT8}, bytes,
@@ -111,9 +109,8 @@ std::unique_ptr<cudf::column> child_chars_from_string_vector(
     thrust::for_each_n(execpol->on(stream),
         thrust::make_counting_iterator<size_type>(0), count,
         [d_strings, d_offsets, d_chars] __device__(size_type idx){
-            string_view d_str = d_strings[idx];
-            if( !d_str.is_null() )
-                memcpy(d_chars + d_offsets[idx], d_str.data(), d_str.size_bytes() );
+            string_view const d_str = d_strings[idx];
+            memcpy(d_chars + d_offsets[idx], d_str.data(), d_str.size_bytes() );
         });
 
     return chars_column;
@@ -126,12 +123,6 @@ std::unique_ptr<column> create_chars_child_column( cudf::size_type strings_count
     cudaStream_t stream)
 {
     CUDF_EXPECTS(null_count <= strings_count, "Invalid null count");
-    // If we have all nulls, a null chars column is allowed.
-    // If all non-null strings are empty strings, we need a non-null chars column.
-    // In this case we set the bytes to 1 to create a minimal one-byte chars column.
-    if( (total_bytes==0) && (null_count < strings_count) )
-        total_bytes = 1; // all entries are empty strings (not nulls)
-    // return chars column
     return make_numeric_column( data_type{INT8}, total_bytes, mask_state::UNALLOCATED, stream, mr );
 }
 

python/cudf/cudf/core/column/string.py

@@ -1911,16 +1911,6 @@ def __init__(self, mask=None, size=None, offset=0, children=()):
             None, size, dtype, mask=mask, offset=offset, children=children
         )
 
-        # For an "all empty" StringColumn (e.g., [""]) libcudf still
-        # needs the chars child column pointer to be non-null:
-        if self.size:
-            if self.children[1].size == 0 and self.null_count != self.size:
-                offsets = self.base_children[0]
-                chars = column_empty(
-                    self.base_children[1].size + 1, dtype="int8"
-                )
-                self.set_base_children((offsets, chars))
-
         # TODO: Remove these once NVStrings is fully deprecated / removed
         self._nvstrings = None
         self._nvcategory = None