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Changelog

2.0-beta-33

tech.v2.datatype namespace has a new function - make-reader - that reifies a reader of the appropriate type. This allows you to make new columns that have nontrivial translations and datatypes much easier than before.
tech.v2.datatype namespace has a new function - ->typed-reader - that typecasts the incoming object into a reader of the appropriate datatype. This means that .read calls will be strongly typed and is useful for building up a set of typed variables before using make-reader above.
Some documentation on the implications of columns, readers, and datatypes.

Issue 52 - CSV columns with empty column names get named after their index. Before they would cause an exception.
tech.datatype added a method to transform a reader into a persistent-vector-like object that derives from clojure.lang.APersistentVector and thus gains benefit from the excellent equality and hash semantics of persistent vectors.

Fixed #38 - set-missing/remove-rows can take infinite seqs - they are trimmed to dataset length.
Fixed #47 - Added columnwise-concat which is a far simpler version of dplyr's https://tidyr.tidyverse.org/reference/pivot_longer.html. This is implemented efficiently in terms of indexed reader concatentation and as such should work on tables of any size.
Fixed #57 - BREAKING PUBLIC API CHANGES - We are getting more strict on the API - if a function is dataset-last (thus appropriate for ->>) then any options must be passed before the dataset. Same is true for the set of functions that are dataset first. We will be more strict about this from now on.

Parsing datetime types now works if the column starts with missing values.
An efficient formulation of java.util.map is introduced for when you have a bitmap of keys and a single value: tech.v2.datatype.bitmap/bitmap-value->bitmap-map. This is used for replace-missing type operations.

brief now does not return missing values. Double or float NaN or INF values from a mapseq result in maps with fewer keys.
Set of columns used for default descriptive stats is reduced to original set as this fits on a small repl nicely. Possible to override. brief overrides this to provide defaults to get more information.
unique-by returns indexes in order.
Fixed #51 - mapseq parsing now follows proper number tower.

Fixed #36 - use key-fn uniformly across all loaded datatypes
Fixed #45 - select can take a map. This does a selection and a projection to new column names.
Fixed #41 - boolean columns failed to convert to doubles.
Fixed #44 - head,tail,shuffle,rand-nth,sample all implemented in format appropriate for ->> operators.

Update tech.datatype with upgraded and fewer dependencies.
- asm 7.1 (was 7.0)
- org.clojure/math.combinatorics 1.6 (was 1.2)
- org.clojure/test.check 1.0.0

Optimized filter. Record of optimization is on zulip. Synopsis is a speedup of like 10-20X depending on how much work you want to do :-). The base filter pathway has a speedup of around 2-4X.

Updated description stats to provide list of distinct elements for categorical columns of length less than 21.
Updated mapseq system to provide nil values for missing data as opposed to the specific column datatype's missing value indicator. This can be overridden by passing in :missing-nil? false as an option.
Added brief function to main namespace so you can get a nice brief description of your dataset when working from the REPL. This prints out better than descriptive-stats.

column->dataset - map a transform function over a column and return a new dataset from the result. It is expected the transform function returns a map.
drop-rows, select-rows, drop-columns - more granular select calls.
append-columns - append a list of columns to a dataset. Used with column->dataset.
column-labeled-mapseq - Create a sequence of maps with a :value and :label members. this flattens the dataset by producing Y maps per row instead of 1 map per row where the maps themselves are labeled with the value in their :value member. This is useful to building vega charts.
->distinct-by-column - take the first row where a given key is present. The arrow form of this indicats the dataset is the first argument.
->sort-by, ->sort-by-column - Forms of these functions for using in (->) dataflows.
interpolate-loess - Produce a new column from a given pair of columns using loess interpolation to create the column. The interpolator is saved as metadata on the new column.

Missing a datetime datatype for parse-str and add-to-container! means a compile time error. Packed durations can now be read from mapseqs.

Support for parsing and working with durations. Strings that look like times - "00:00:12" will be parsed into hh:mm:ss durations. The value can have a negative sign in front. This is in addition to the duration's native serialization string type.
Added short test for tensors in datasets. This means that the venerable print-table is no longer enough as it doesn't account for multiline strings and thus datatets with really complex things will not print correctly for a time.

Various fixes related to parsing and working with open data.
tech.ml.dataset.column/parse-column - given a string column that failed to parse for some reason, you can force the system to attempt to parse it using, for instance, relaxed parsing semantics where failures simply record the failure in metadata.
relaxed parsing in general is supported across all input types.

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