Search method and search apparatus

A search method comprising:

• encoding, by a processor, a file that includes a plurality of records each including a plurality of items separated by delimiters into codes, in units of elements included in the plurality of items of the plurality of records, with use of an encoding dictionary indicating corresponding relationships between the elements and the codes;
• generating, by the processor, an index that associates the elements with positions of the respective elements in the file, the index including a first bit string for each of characters that appear in the file, the first bit string indicating positions where the each character appears;
• generating, by the processor, mask information indicating a range of a specific search target item among the plurality of items, in the file, the mask information being a mask bit string of mask bits corresponding to the respective elements in the file, a range of the mask bits with a predetermined value being the range of the specific search target item;
• and
• searching for, by the processor, one or more element strings within the range of the specific search target indicated by the mask information satisfying a search condition from the elements in the file, based on the index, an intermediate search result of the searching being a second bit string indicating positions where the one or more first element strings satisfying the search condition appear;
• performing, by the processor, a bitwise AND operation between the second bit string and the mask bit string;
• and
• outputting a result of the bitwise AND operation as a search result indicating positions where one or more second element strings satisfying the search condition appear within the range of the specific search target item.

A search apparatus comprising:

• a memory configured to store a file that includes a plurality of records each including a plurality of items separated by delimiters;
• and
• a processor configured to perform a process including:
• encoding the file into codes, in units of elements included in the plurality of items of the plurality of records, with use of an encoding dictionary indicating corresponding relationships between the elements and the codes;
• generating an index that associates the elements with positions of the respective elements in the file, the index including a first bit string for each of characters that appear in the file, the first bit string indicating positions where the each character appears;
• generating mask information indicating a range of a specific search target item among the plurality of items, in the file, the mask information being a mask bit string of mask bits corresponding to the respective elements in the file, a range of the mask bits with a predetermined value being the range of the specific search target item;
• and
• searching for one or more element strings within the range of the specific search target indicated by the mask information satisfying a search condition from the elements in the file, based on the index, an intermediate search result of the searching being a second bit string indicating positions where the one or more first element strings satisfying the search condition appear;
• performing a bitwise AND operation between the second bit string and the mask bit string;
• and
• outputting a result of the bitwise AND operation as a search result indicating positions where one or more second element strings satisfying the search condition appear within the range of the specific search target item.