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Quantitative Finance · Glossaire

Qu'est-ce que « Validity bitmap » ?

Definition 3.3 Research, Data and Risk Platforms · Chapitre 3 — Columnar Formats

The validity bitmap of a column is a buffer holding one bit per value, set when the value is present and clear when it is null, numbered from the least significant bit of each byte; a column with no null may omit it.

Buffers of the first 1 000 rows of three columns of the chapter’s quotes in the in-memory columnar format: an integer column with no null needs no validity bitmap; a nullable string column has a bitmap, n+1 offsets and a data buffer holding only the 49 characters of its 49 present values; a dictionary column holds 4-byte indices into 50 distinct symbols. Data: pl_colfmt.arrow_buffers.
Figure 3.2. Buffers of the first 1 000 rows of three columns of the chapter’s quotes in the in-memory columnar format: an integer column with no null needs no validity bitmap; a nullable string column has a bitmap, n+1n+1 offsets and a data buffer holding only the 49 characters of its 49 present values; a dictionary column holds 4-byte indices into 50 distinct symbols. Data: pl_colfmt.arrow_buffers.
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