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minor docs changes
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@ritchie46
ritchie46 committed Aug 27, 2020
1 parent 8a7ca91 commit 9f32ecd
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176 changes: 98 additions & 78 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -33,116 +33,136 @@ structs in that order. For `ChunkedArray` a lot of functionality is also defined
### Read and write CSV | JSON | IPC | Parquet

```rust
use polars::prelude::*;
use std::fs::File;

fn example() -> Result<DataFrame> {
let file = File::open("iris.csv").expect("could not open file");

CsvReader::new(file)
.infer_schema(None)
.has_header(true)
.finish()
}
use polars::prelude::*;
use std::fs::File;

fn example() -> Result<DataFrame> {
let file = File::open("iris.csv")
.expect("could not open file");

CsvReader::new(file)
.infer_schema(None)
.has_header(true)
.finish()
}
```

### Joins

```rust
use polars::prelude::*;

// Create first df.
let s0 = Series::new("days", &[0, 1, 2, 3, 4]);
let s1 = Series::new("temp", &[22.1, 19.9, 7., 2., 3.]);
let temp = DataFrame::new(vec![s0, s1]).unwrap();

// Create second df.
let s0 = Series::new("days", &[1, 2]);
let s1 = Series::new("rain", &[0.1, 0.2]);
let rain = DataFrame::new(vec![s0, s1]).unwrap();

// Left join on days column.
let joined = temp.left_join(&rain, "days", "days");
println!("{}", joined.unwrap())
use polars::prelude::*;

fn join() -> Result<DataFrame> {
// Create first df.
let s0 = Series::new("days", &[0, 1, 2, 3, 4]);
let s1 = Series::new("temp", &[22.1, 19.9, 7., 2., 3.]);
let temp = DataFrame::new(vec![s0, s1])?;

// Create second df.
let s0 = Series::new("days", &[1, 2]);
let s1 = Series::new("rain", &[0.1, 0.2]);
let rain = DataFrame::new(vec![s0, s1])?;

// Left join on days column.
temp.left_join(&rain, "days", "days")
}
println!("{}", join().unwrap());
```

```text
+------+------+------+
| days | temp | rain |
| --- | --- | --- |
| i32 | f64 | f64 |
+======+======+======+
| 0 | 22.1 | null |
+------+------+------+
| 1 | 19.9 | 0.1 |
+------+------+------+
| 2 | 7 | 0.2 |
+------+------+------+
| 3 | 2 | null |
+------+------+------+
| 4 | 3 | null |
+------+------+------+
+------+------+------+
| days | temp | rain |
| --- | --- | --- |
| i32 | f64 | f64 |
+======+======+======+
| 0 | 22.1 | null |
+------+------+------+
| 1 | 19.9 | 0.1 |
+------+------+------+
| 2 | 7 | 0.2 |
+------+------+------+
| 3 | 2 | null |
+------+------+------+
| 4 | 3 | null |
+------+------+------+
```

### GroupBys

```rust
use polars::prelude::*;
fn groupby_sum(df: &DataFrame) -> Result<DataFrame> {
df.groupby("column_name")?
.select("agg_column_name")
.sum()
}
use polars::prelude::*;
fn groupby_sum(df: &DataFrame) -> Result<DataFrame> {
df.groupby("column_name")?
.select("agg_column_name")
.sum()
}
```

### Arithmetic
```rust
use polars::prelude::*;
let s: Series = [1, 2, 3].iter().collect();
let s_squared = &s * &s;
use polars::prelude::*;
let s: Series = [1, 2, 3].iter().collect();
let s_squared = &s * &s;
```

### Rust iterators

```rust
use polars::prelude::*;

let s: Series = [1, 2, 3].iter().collect();
let s_squared: Series = s.i32()
.expect("datatype mismatch")
.into_iter()
.map(|optional_v| {
match optional_v {
Some(v) => Some(v * v),
None => None, // null value
}
}).collect();
use polars::prelude::*;
let s: Series = [1, 2, 3].iter().collect();
let s_squared: Series = s.i32()
.expect("datatype mismatch")
.into_iter()
.map(|optional_v| {
match optional_v {
Some(v) => Some(v * v),
None => None, // null value
}
}).collect();
```

### Apply custom closures
```rust
use polars::prelude::*;

let s: Series = Series::new("values", [Some(1.0), None, Some(3.0)]);
// null values are ignored automatically
let squared = s.f64()
.unwrap()
.apply(|value| value.powf(2.0))
.into_series();

assert_eq!(Vec::from(squared.f64().unwrap()), &[Some(1.0), None, Some(9.0)])
use polars::prelude::*;
let s: Series = Series::new("values", [Some(1.0), None, Some(3.0)]);
// null values are ignored automatically
let squared = s.f64()
.unwrap()
.apply(|value| value.powf(2.0))
.into_series();
assert_eq!(Vec::from(squared.f64().unwrap()), &[Some(1.0), None, Some(9.0)])
```

### Comparisons

```rust
use polars::prelude::*;
use itertools::Itertools;
let s = Series::new("dollars", &[1, 2, 3]);
let mask = s.eq(1);
let valid = [true, false, false].iter();
use polars::prelude::*;
use itertools::Itertools;
let s = Series::new("dollars", &[1, 2, 3]);
let mask = s.eq(1);
let valid = [true, false, false].iter();

assert_eq!(Vec::from(mask.bool().unwrap()), &[Some(true), Some(false), Some(false)]);
```

assert_eq!(Vec::from(mask.bool().unwrap()), &[Some(true), Some(false), Some(false)]);
## Temporal data types

```rust
let dates = &[
"2020-08-21",
"2020-08-21",
"2020-08-22",
"2020-08-23",
"2020-08-22",
];
// date format
let fmt = "%Y-%m-%d";
// create date series
let s0 = Date32Chunked::parse_from_str_slice("date", dates, fmt)
.into_series();
```

## And more...
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46 changes: 34 additions & 12 deletions polars/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,8 @@
//! use std::fs::File;
//!
//! fn example() -> Result<DataFrame> {
//! let file = File::open("iris.csv").expect("could not open file");
//! let file = File::open("iris.csv")
//! .expect("could not read file");
//!
//! CsvReader::new(file)
//! .infer_schema(None)
Expand All @@ -36,19 +37,22 @@
//! ```
//! use polars::prelude::*;
//!
//! // Create first df.
//! let s0 = Series::new("days", &[0, 1, 2, 3, 4]);
//! let s1 = Series::new("temp", &[22.1, 19.9, 7., 2., 3.]);
//! let temp = DataFrame::new(vec![s0, s1]).unwrap();
//! fn join() -> Result<DataFrame> {
//! // Create first df.
//! let s0 = Series::new("days", &[0, 1, 2, 3, 4]);
//! let s1 = Series::new("temp", &[22.1, 19.9, 7., 2., 3.]);
//! let temp = DataFrame::new(vec![s0, s1])?;
//!
//! // Create second df.
//! let s0 = Series::new("days", &[1, 2]);
//! let s1 = Series::new("rain", &[0.1, 0.2]);
//! let rain = DataFrame::new(vec![s0, s1]).unwrap();
//! // Create second df.
//! let s0 = Series::new("days", &[1, 2]);
//! let s1 = Series::new("rain", &[0.1, 0.2]);
//! let rain = DataFrame::new(vec![s0, s1])?;
//!
//! // Left join on days column.
//! let joined = temp.left_join(&rain, "days", "days");
//! println!("{}", joined.unwrap())
//! // Left join on days column.
//! temp.left_join(&rain, "days", "days")
//! }
//!
//! println!("{}", join().unwrap())
//! ```
//!
//! ```text
Expand Down Expand Up @@ -134,6 +138,24 @@
//! assert_eq!(Vec::from(mask.bool().unwrap()), &[Some(true), Some(false), Some(false)]);
//! ```
//!
//! ## Temporal data types
//!
//! ```rust
//! # use polars::prelude::*;
//! let dates = &[
//! "2020-08-21",
//! "2020-08-21",
//! "2020-08-22",
//! "2020-08-23",
//! "2020-08-22",
//! ];
//! // date format
//! let fmt = "%Y-%m-%d";
//! // create date series
//! let s0 = Date32Chunked::parse_from_str_slice("date", dates, fmt)
//! .into_series();
//! ```
//!
//! ## And more...
//!
//! * [DataFrame](frame/struct.DataFrame.html)
Expand Down

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