compress

Syntax

compress(X, [method='lz4'])

Arguments

X is a vector or a table.

method (optional) is a string indicating the compression algorithm. The available options are:

  • "lz4" (by default) is suitable for almost all data types. Although the "lz4" method may not achieve the highest compression ratio, it provides fast compression and decompression speeds.

  • "delta" option applies delta-of-delta algorithm, which is particularly suitable for data types like SHORT, INT, LONG, and date/time data.

  • "zstd" is also suitable for almost all data types. It provides a higher compression ratio compared to "lz4", but the compression and decompression speed is about half as fast as "lz4".

  • “chimp“ is suitable for DOUBLE type data with decimal parts not exceeding three digits in length.

Details

Compress a vector or a table with the specified compression algorithm. The compressed variable needs to be decompressed with function decompress before it can be used in a calculation.

Examples

x=1..100000000
y=compress(x, "delta");

y.typestr();
// output: HUGE COMPRESSED VECTOR

z=compress(x, "zstd");
z.typestr();
// output: HUGE COMPRESSED VECTOR

select name, bytes from objs() where name in `x`y;
name bytes
x 402653952
y 13634544

Please note that if function size is applied on the compressed vector y, the result is the length of the compressed vector y instead of the original vector x. To extract information about x from y, we need to decompress y first.

y.size();
// output: 12670932

z=decompress(y);
z.size();
// output: 100000000

Related functions: decompress