add readme

Author: gabysbrain

README.md

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+# purescript-dataframe
+
+[![Latest release](http://img.shields.io/github/release/gabysbrain/purescript-dataframe.svg)](https://github.com/gabysbrain/purescript-dataframe/releases)
+
+A datastructure designed to be used with queries as well as a type for
+queries. There is also semantics for combining the queries.
+
+# Example
+
+```purescript
+main = do
+  let df = init [1, 2, 3, 4, 5, 6, 7]
+      q = filter (\x -> x > 3) `chain`
+          mutate show `chain`
+          trim 3
+  putStrLn $ runQuery q df
+```
+
+# Getting started
+
+## Installation
+
+```
+bower install purescript-dataframe
+```
+
+## Queries
+
+The idea of a Query type is that we want to have a type-safe way to chain
+operations on dataframes and we want to maintain the original dataset
+throughout the query. In other data processing languages this is a common
+source of error, especially when mutating rows. 
+
+The set of dataframe operations are based on what's offered by the
+[dplyr](https://github.com/tidyverse/dplyr) R package.
+
+* `filter :: forall r. (r -> Boolean) -> Query (DataFrame r) (Dataframe r)` 
+  filter rows of the DataFrame
+* `group :: forall r g. Ord g => (r -> g) -> Query (DataFrame r) (DataFrame {group :: g, data :: Dataframe r})` 
+  group the rows of the dataframe by some grouping method
+* `count :: forall r g. Ord g => (r -> g) -> Query (DataFrame r) (DataFrame {group :: g, count :: Int})` 
+  group the rows of the dataframe and count the size of the groups
+* `summarize :: forall r x. (r -> x) -> Query (DataFrame r) (Array x)` 
+  convert each row of the dataframe to some type and return an array
+* `mutate :: forall r s. (r -> s) -> Query (DataFrame r) (Dataframe s)` 
+  change each row of the dataframe to some other type
+* `sort :: forall r. (r -> r -> Ordering) -> Query (DataFrame r) (Dataframe r)` 
+  sort the rows of the dataframe given the ordering function
+* `trim :: forall r. Int -> Query (DataFrame r) (Dataframe r)` 
+  keep only the first n rows of the DataFrame
+
+The `chain :: forall r s t. Query r s -> Query s t -> Query r t` function
+allows us to chain queries and keep the original context.
+
+# API Docs
+
+API documentation is [published on Pursuit](http://pursuit.purescript.org/packages/purescript-dataframe).
+
+# Todos
+
+* DataFrames should be able to operate either as a set of columns or a set of rows.
+* Queries should do caching
+