Trait csvsc::prelude::RowStream [−][src]
This trait describes de behaviour of every component in the CSV transformation chain. Functions provided by this trait help construct the chain and can be chained.
Implement this trait to extend csvsc
with your own processors.
Required methods
fn headers(&self) -> &Headers
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Must return headers as they are in this point of the chain. For example
if implementor adds a column, its headers()
function must return the
new headers including the one just added.
Provided methods
fn add(self, column: ColSpec) -> Result<Add<Self>> where
Self: Sized,
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Self: Sized,
Add a column to each row of the stream.
New columns can be build arbitrarily from previous columns or from a specific column using a regular expression.
use csvsc::prelude::*; use encoding::all::UTF_8; let mut chain = InputStreamBuilder::from_paths(&["test/assets/1.csv"]) .unwrap().build().unwrap() .add( Column::with_name("new column") .from_all_previous() .definition("{old col1} - {old col2}") ).unwrap();
See Column
for options.
If you want to add a constant value or have some other requirement take
a look at .add_with()
.
fn del(self, columns: Vec<&str>) -> Del<'_, Self> where
Self: Sized,
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Self: Sized,
Deletes the specified columns from each row of the stream. If you have
too many columns to delete perhaps instead use RowStream::select
.
fn select(self, columns: Vec<&str>) -> Select<'_, Self> where
Self: Sized,
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Self: Sized,
Outputs only the selected columns, ignoring the rest.
If you only want do delete specific columns take a look at
RowStream::del
.
fn add_with<F>(
self,
colname: &str,
f: F
) -> Result<AddWith<Self, F>, BuildError> where
Self: Sized,
F: FnMut(&Headers, &Row) -> Result<String>,
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self,
colname: &str,
f: F
) -> Result<AddWith<Self, F>, BuildError> where
Self: Sized,
F: FnMut(&Headers, &Row) -> Result<String>,
Adds a column to each row of the stream using a closure to compute its value.
This you can use to add a constant value also.
Example
use csvsc::prelude::*; use encoding::all::UTF_8; let mut chain = InputStreamBuilder::from_paths(&["test/assets/1.csv"]) .unwrap().build().unwrap() .add_with("new col", |headers, row| { Ok("value".into()) }).unwrap();
fn reduce(self, columns: Vec<Box<dyn Aggregate>>) -> Result<Reduce<Self>> where
Self: Sized,
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Self: Sized,
Reduce all the incoming stream into one row, computing some aggregates in the way. All the stream collapses into one row.
The final row contains only the result of reducers and no other column
but you might preserve a column using the .last()
aggregate.
You’ll likely be using this inside a .group()
or .adjacent_group()
.
Example
use csvsc::prelude::*; use encoding::all::UTF_8; let mut chain = InputStreamBuilder::from_paths(&["test/assets/chicken_north.csv"]) .unwrap().build().unwrap() .group(["month"], |row_stream| { row_stream .reduce(vec![ Reducer::with_name("avg").of_column("eggs per week").average().unwrap(), ]).unwrap() });
See Reducer
for built-in aggregates.
fn adjacent_group<F, R, G>(self, grouping: G, f: F) -> AdjacentGroup<Self, F, G> where
F: Fn(MockStream<IntoIter<RowResult>>) -> R,
R: RowStream,
G: GroupCriteria,
Self: Sized,
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F: Fn(MockStream<IntoIter<RowResult>>) -> R,
R: RowStream,
G: GroupCriteria,
Self: Sized,
Groups rows by the given criteria, but assuming a “group” is a set of adjacent rows.
This means that sets of rows that meet the same criteria but are not adjacent will not be grouped together. Only use it if you are sure that your data follows this pattern and you want to take advantage of it.
An interesting advantage of using this is that only one group is kept in memory at a time.
See RowStream::group
for more details.
Example
Consider a file test/assets/groups.csv
with this contents. Notice that
there are four adjacent groups that have the same value for column
name
: two with value a
and two with b
.
name,value
a,1
a,1
b,2
b,2
a,3
a,3
b,4
b,4
Then the following code works as expected, generating an average for all
of the four adjacent groups that have the same value for column name
.
use csvsc::prelude::*; let mut rows = InputStreamBuilder::from_paths(&["test/assets/groups.csv"]).unwrap().build().unwrap() .adjacent_group(["name"], |row_stream| { row_stream .reduce(vec![ Reducer::with_name("name").of_column("name").last("").unwrap(), Reducer::with_name("avg").of_column("value").average().unwrap(), ]).unwrap() }) .into_iter(); assert_eq!(rows.next().unwrap().unwrap(), Row::from(vec!["a", "1"])); assert_eq!(rows.next().unwrap().unwrap(), Row::from(vec!["b", "2"])); assert_eq!(rows.next().unwrap().unwrap(), Row::from(vec!["a", "3"])); assert_eq!(rows.next().unwrap().unwrap(), Row::from(vec!["b", "4"]));
fn group<F, R, G>(self, grouping: G, f: F) -> Group<Self, F, G> where
F: Fn(MockStream<IntoIter<RowResult>>) -> R,
R: RowStream,
G: GroupCriteria,
Self: Sized,
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F: Fn(MockStream<IntoIter<RowResult>>) -> R,
R: RowStream,
G: GroupCriteria,
Self: Sized,
Groups rows by the given criteria. You’ll be given a RowStream instance as the first argument of a closure that you can use to further process the grouped rows.
The first argument is the group criteria and it can be any of:
- A slice of
&str
:&["foo", "bar"]
, - an array of
&str
:["foo", "bar"]
, - a closure
Fn(&Headers, &Row) -> Hash
, - any type that implements
GroupCriteria
In the first two cases the &str
s are treated as column names. Rows
having the same values for the specified columns will belong to the same
group. Strings that don’t match any column name will be ignored.
In the closure case you’ll be given the headers and every row and you must return a hashable type that identifies the group where that row belongs.
GroupCriteria
is a trait you can
implement for your own types if you want to use them as grouping
criteria.
Example
Consider the following file:
name,value
a,1
a,1
b,2
b,2
a,3
a,3
b,4
b,4
Then we can group for example using the column name
and get the
following results:
use csvsc::prelude::*; let mut rows: Vec<_> = InputStreamBuilder::from_paths(&["test/assets/groups.csv"]).unwrap().build().unwrap() .group(["name"], |row_stream| { row_stream .reduce(vec![ Reducer::with_name("name").of_column("name").last("").unwrap(), Reducer::with_name("avg").of_column("value").average().unwrap(), ]).unwrap() }) .into_iter() .filter_map(|r| r.ok()) .collect(); rows.sort_by_key(|row| row.get(0).unwrap().to_string()); assert_eq!(rows[0], Row::from(vec!["a", "2"])); assert_eq!(rows[1], Row::from(vec!["b", "3"]));
Grouping by closure
If you decide that you need an arbitrary grouping criteria you can use a closure that returns a hashable type like this:
use csvsc::prelude::*; let mut rows: Vec<_> = InputStreamBuilder::from_paths(&["test/assets/groups.csv"]).unwrap().build().unwrap() .group(|headers: &Headers, row: &Row| { headers.get_field(row, "name").unwrap().to_string() }, |row_stream| { row_stream .reduce(vec![ Reducer::with_name("name").of_column("name").last("").unwrap(), Reducer::with_name("avg").of_column("value").average().unwrap(), ]).unwrap() }) .into_iter() .filter_map(|r| r.ok()) .collect(); rows.sort_by_key(|row| row.get(0).unwrap().to_string()); assert_eq!(rows[0], Row::from(vec!["a", "2"])); assert_eq!(rows[1], Row::from(vec!["b", "3"]));
fn flush<T>(self, target: T) -> Result<Flush<Self, T>> where
Self: Sized,
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Self: Sized,
When consumed, writes to destination specified by the column given in
the first argument. Other than that this behaves like an id(x)
function so you can specify more links in the chain and even more
flushers.
fn review<F>(self, f: F) -> Inspect<Self, F> where
Self: Sized,
F: FnMut(&Headers, &RowResult),
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Self: Sized,
F: FnMut(&Headers, &RowResult),
Mostly for debugging, calls a closure on each element. Behaves like the identity function on the stream returning each row untouched.
fn rename(self, old_name: &str, new_name: &str) -> Rename<Self> where
Self: Sized,
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Self: Sized,
Renames some columns
fn map_row<F, H, R>(self, f: F, header_map: H) -> MapRow<Self, F> where
Self: Sized,
F: Fn(&Headers, &Row) -> Result<R>,
H: Fn(&Headers) -> Headers,
R: Iterator<Item = RowResult>,
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Self: Sized,
F: Fn(&Headers, &Row) -> Result<R>,
H: Fn(&Headers) -> Headers,
R: Iterator<Item = RowResult>,
Apply a function to every row and use the return values to build the row stream.
This method accepts a closure that must return an iterator over RowResult values, this means that you can create more rows out of a single one.
You’re responsible of providing the new headers and for that you need to use the second closure, that maps the old headers to the new ones.
Example
use csvsc::prelude::*; use encoding::all::UTF_8; InputStreamBuilder::from_paths(&["test/assets/1.csv"]) .unwrap().build().unwrap() .map_row(|_headers, row| { // Go creative here in the creation of your new row(s) Ok(vec![ Ok(row.clone()) ].into_iter()) }, |old_headers| { // be responsible and provide proper headers from the old ones old_headers.clone() }) .into_iter();
fn map_col<F>(self, col: &str, f: F) -> MapCol<Self, F> where
Self: Sized,
F: Fn(&str) -> Result<String>,
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Self: Sized,
F: Fn(&str) -> Result<String>,
Apply a function to a single column of the stream, this function dones’t fail if the column dones’t exist.
fn filter_col<F>(self, col: &str, f: F) -> Result<FilterCol<Self, F>> where
Self: Sized,
F: Fn(&str) -> bool,
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Self: Sized,
F: Fn(&str) -> bool,
filter entire rows out depending on one column’s value and a condition, leaving errored rows untouched.
fn filter_row<F>(self, f: F) -> FilterRow<Self, F> where
Self: Sized,
F: Fn(&Headers, &Row) -> bool,
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Self: Sized,
F: Fn(&Headers, &Row) -> bool,
filter entire rows out depending on one column’s value and a condition, leaving errored rows untouched.
Implementors
impl RowStream for InputStream
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impl<I> RowStream for Add<I> where
I: RowStream,
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I: RowStream,
impl<I> RowStream for MockStream<I> where
MockStream<I>: IntoIterator<Item = RowResult>,
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MockStream<I>: IntoIterator<Item = RowResult>,