Minor formatting fixes

This commit is contained in:
Alan Bernstein 2018-05-11 14:52:35 -05:00
parent 22cb90c1a3
commit 2abca951e7
2 changed files with 3 additions and 3 deletions

View file

@ -87,7 +87,7 @@ This is one major component of Pilosa's ability to combine relationships from mu
#### Ranked
Ranked Frames maintain a sorted cache of column counts by Row ID (yielding the top rows by columns with a bit set in each). This cache facilitates the TopN query. The cache size defaults to 50,000 and can be set at Frame creation.
Ranked Frames maintain a sorted cache of column counts by Row ID (yielding the top rows by columns with a bit set in each). This cache facilitates the TopN query. The cache size defaults to 50,000 and can be set at Frame creation.
![ranked frame diagram](/img/docs/frame-ranked.svg)
*Ranked frame diagram*

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@ -65,13 +65,13 @@ Each column that we want to use must be mapped to a combination of frames and ro
##### 0 columns → 1 frame
cab_type: contains one row for each type of cab. Each column, representing one ride, has a bit set in exactly one row of this frame. The mapping is a simple enumeration, for example yellow=0, green=1, etc. The values of the bits in this frame are determined by the source of the data. That is, we're importing data from several disparate sources: NYC yellow taxi cabs, NYC green taxi cabs, and Uber cars. For each source, the single row to be set in the cab_type frame is constant.
**cab_type**: contains one row for each type of cab. Each column, representing one ride, has a bit set in exactly one row of this frame. The mapping is a simple enumeration, for example yellow=0, green=1, etc. The values of the bits in this frame are determined by the source of the data. That is, we're importing data from several disparate sources: NYC yellow taxi cabs, NYC green taxi cabs, and Uber cars. For each source, the single row to be set in the cab_type frame is constant.
##### 1 column → 1 frame
The following three frames are mapped in a simple direct way from single columns of the original data.
dist_miles: each row represents rides of a certain distance. The mapping is simple: as an example, row 1 represents rides with a distance in the interval [0.5, 1.5]. That is, we round the floating point value of distance to an integer, and use that as the row ID directly. Generally, the mapping from a floating point value to a row ID could be arbitrary. The rounding mapping is concise to implement, which simplifies importing and analysis. As an added bonus, it's human-readable. We'll see this pattern used several times.
**dist_miles:** each row represents rides of a certain distance. The mapping is simple: as an example, row 1 represents rides with a distance in the interval [0.5, 1.5]. That is, we round the floating point value of distance to an integer, and use that as the row ID directly. Generally, the mapping from a floating point value to a row ID could be arbitrary. The rounding mapping is concise to implement, which simplifies importing and analysis. As an added bonus, it's human-readable. We'll see this pattern used several times.
In PDK parlance, we define a Mapper, which is simply a function that returns integer row IDs. PDK has a number of predefined mappers that can be described with a few parameters. One of these is LinearFloatMapper, which applies a linear function to the input, and casts it to an integer, so the rounding is handled implicitly. In code:
```go