Count distinct floats

[pjmore]

Which issue does this PR close?

Closes #199 .

What changes are included in this PR?

Modified try_from_array method on ScalarValue and added tests to physical_plan/distinct_expressions.rs

The tests cover all of the floating point weirdness that I could think of, namely NaN, the infinities, and subnormal numbers, but if I missed any I'm happy to add tests for them.

Are there any user-facing changes?

No

[Dandandan]

Looks good, thanks @pjmore !

[codecov-commenter]

Codecov Report

Merging #252 (774d7b4) into master (e271e4d) will increase coverage by 0.00%.
The diff coverage is 70.00%.

@@           Coverage Diff           @@
##           master     #252   +/-   ##
=======================================
  Coverage   76.80%   76.81%           
=======================================
  Files         133      133           
  Lines       23284    23294   +10     
=======================================
+ Hits        17884    17894   +10     
  Misses       5400     5400           

Impacted Files	Coverage Δ
datafusion/src/scalar.rs	54.36% <0.00%> (+0.22%)	⬆️
...tafusion/src/physical_plan/distinct_expressions.rs	90.80% <87.50%> (-0.11%)	⬇️
datafusion/src/physical_plan/group_scalar.rs	58.82% <0.00%> (+1.17%)	⬆️

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[alamb]

I tried it out locally and it works great. Thank you @pjmore !

alamb@ip-10-0-0-124:~/Software/arrow-datafusion$  echo "foo,1.23" > /tmp/foo.csv
alamb@ip-10-0-0-124:~/Software/arrow-datafusion$ cargo run -p datafusion-cli
    Finished dev [unoptimized + debuginfo] target(s) in 0.13s
     Running `target/debug/datafusion-cli`
> CREATE EXTERNAL TABLE t (a varchar, b float) STORED AS CSV LOCATION '/tmp/foo.csv';
0 rows in set. Query took 0 seconds.

> select count(distinct a) from t;
+-------------------+
| COUNT(DISTINCT a) |
+-------------------+
| 1                 |
+-------------------+
1 rows in set. Query took 0 seconds.
> select count(distinct b) from t;
+-------------------+
| COUNT(DISTINCT b) |
+-------------------+
| 1                 |
+-------------------+
1 rows in set. Query took 0 seconds.

[Dandandan]

Thanks again @pjmore !

[alamb]

🎉