Struct perspective_js::View

pub struct View(/* private fields */);

The View struct is Perspective’s query and serialization interface. It represents a query on the Table’s dataset and is always created from an existing Table instance via the Table::view method. .

const table = await perspective.table({
    id: [1, 2, 3, 4],
    name: ["a", "b", "c", "d"],
});

const view = await table.view({ columns: ["name"] });
const json = await view.to_json();
await view.delete();

table = perspective.Table({
  "id": [1, 2, 3, 4],
  "name": ["a", "b", "c", "d"]
});

view = table.view(columns=["name"])
arrow = view.to_arrow()
view.delete()

let opts = TableInitOptions::default();
let data = TableData::Update(UpdateData::Csv("x,y\n1,2\n3,4".into()));
let table = client.table(data, opts).await?;

let view = table.view(None).await?;
let arrow = view.to_arrow().await?;
view.delete().await?;

Views are immutable with respect to the arguments provided to the Table::view method; to change these parameters, you must create a new View on the same Table. However, each View is live with respect to the Table’s data, and will (within a conflation window) update with the latest state as its parent Table updates, including incrementally recalculating all aggregates, pivots, filters, etc. View query parameters are composable, in that each parameter works independently and in conjunction with each other, and there is no limit to the number of pivots, filters, etc. which can be applied.

Querying data with Table::view

To query the table, create a Table::view on the table instance with an optional configuration object. A Table can have as many Views associated with it as you need - Perspective conserves memory by relying on a single Table to power multiple Views concurrently:

const view = await table.view({
    columns: ["Sales"],
    aggregates: { Sales: "sum" },
    group_by: ["Region", "Country"],
    filter: [["Category", "in", ["Furniture", "Technology"]]],
});

view = table.view(
  columns=["Sales"],
  aggregates={"Sales": "sum"},
  group_by=["Region", "Country"],
  filter=[["Category", "in", ["Furniture", "Technology"]]]
)

use crate::config::*;
let view = table
    .view(Some(ViewConfigUpdate {
        columns: Some(vec![Some("Sales".into())]),
        aggregates: Some(HashMap::from_iter(vec![("Sales".into(), "sum".into())])),
        group_by: Some(vec!["Region".into(), "Country".into()]),
        filter: Some(vec![Filter::new("Category", "in", &[
            "Furniture",
            "Technology",
        ])]),
        ..ViewConfigUpdate::default()
    }))
    .await?;

Group By

A group by groups the dataset by the unique values of each column used as a group by - a close analogue in SQL to the GROUP BY statement. The underlying dataset is aggregated to show the values belonging to each group, and a total row is calculated for each group, showing the currently selected aggregated value (e.g. sum) of the column. Group by are useful for hierarchies, categorizing data and attributing values, i.e. showing the number of units sold based on State and City. In Perspective, group by are represented as an array of string column names to pivot, are applied in the order provided; For example, a group by of ["State", "City", "Postal Code"] shows the values for each Postal Code, which are grouped by City, which are in turn grouped by State.

Example

const view = await table.view({ group_by: ["a", "c"] });

view = table.view(group_by=["a", "c"])

let view = table.view(Some(ViewConfigUpdate {
    group_by: Some(vec!["a".into(), "c".into()]),
    ..ViewConfigUpdate::default()
})).await?;

Split By

A split by splits the dataset by the unique values of each column used as a split by. The underlying dataset is not aggregated, and a new column is created for each unique value of the split by. Each newly created column contains the parts of the dataset that correspond to the column header, i.e. a View that has ["State"] as its split by will have a new column for each state. In Perspective, Split By are represented as an array of string column names to pivot:

Example

const view = await table.view({ split_by: ["a", "c"] });

view = table.view(split_by=["a", "c"])

let view = table.view(Some(ViewConfigUpdate {
    split_by: Some(vec!["a".into(), "c".into()]),
    ..ViewConfigUpdate::default()
})).await?;

Aggregates

Aggregates perform a calculation over an entire column, and are displayed when one or more Group By are applied to the View. Aggregates can be specified by the user, or Perspective will use the following sensible default aggregates based on column type:

• “sum” for integer and float columns
• “count” for all other columns

Perspective provides a selection of aggregate functions that can be applied to columns in the View constructor using a dictionary of column name to aggregate function name.

Example

const view = await table.view({
    aggregates: {
        a: "avg",
        b: "distinct count",
    },
});

view = table.view(
  aggregates={
    "a": "avg",
    "b": "distinct count"
  }
)

Columns

The columns property specifies which columns should be included in the View’s output. This allows users to show or hide a specific subset of columns, as well as control the order in which columns appear to the user. This is represented in Perspective as an array of string column names:

Example

const view = await table.view({
    columns: ["a"],
});

view = table.view(columns=["a"])

Sort

The sort property specifies columns on which the query should be sorted, analogous to ORDER BY in SQL. A column can be sorted regardless of its data type, and sorts can be applied in ascending or descending order. Perspective represents sort as an array of arrays, with the values of each inner array being a string column name and a string sort direction. When column-pivots are applied, the additional sort directions "col asc" and "col desc" will determine the order of pivot columns groups.

Example

const view = await table.view({
    sort: [["a", "asc"]],
});

view = table.view(sort=[["a", "asc"]])

Filter

The filter property specifies columns on which the query can be filtered, returning rows that pass the specified filter condition. This is analogous to the WHERE clause in SQL. There is no limit on the number of columns where filter is applied, but the resulting dataset is one that passes all the filter conditions, i.e. the filters are joined with an AND condition.

Perspective represents filter as an array of arrays, with the values of each inner array being a string column name, a string filter operator, and a filter operand in the type of the column:

Example

const view = await table.view({
    filter: [["a", "<", 100]],
});

view = table.view(filter=[["a", "<", 100]])

Expressions

The expressions property specifies new columns in Perspective that are created using existing column values or arbitary scalar values defined within the expression. In <perspective-viewer>, expressions are added using the “New Column” button in the side panel.

A custom name can be added to an expression by making the first line a comment:

Example

const view = await table.view({
    expressions: { '"a" + "b"': '"a" + "b"' },
});

view = table.view(expressions=['"a" + "b"'])

Flattening a Table::view into a Table

In Javascript, a Table can be constructed on a Table::view instance, which will return a new Table based on the Table::view’s dataset, and all future updates that affect the Table::view will be forwarded to the new Table. This is particularly useful for implementing a Client/Server Replicated design, by serializing the View to an arrow and setting up an on_update callback.

Example

const worker1 = perspective.worker();
const table = await worker.table(data);
const view = await table.view({ filter: [["State", "==", "Texas"]] });
const table2 = await worker.table(view);
table.update([{ State: "Texas", City: "Austin" }]);

table = perspective.Table(data);
view = table.view(filter=[["State", "==", "Texas"]])
table2 = perspective.Table(view.to_arrow());

def updater(port, delta):
    table2.update(delta)

view.on_update(updater, mode="Row")
table.update([{"State": "Texas", "City": "Austin"}])

let opts = TableInitOptions::default();
let data = TableData::Update(UpdateData::Csv("x,y\n1,2\n3,4".into()));
let table = client.table(data, opts).await?;
let view = table.view(None).await?;
let table2 = client.table(TableData::View(view)).await?;
table.update(data).await?;

Implementations

impl View

pub async fn column_paths(&self) -> ApiResult<JsValue>

Returns an array of strings containing the column paths of the View without any of the source columns.

A column path shows the columns that a given cell belongs to after pivots are applied.

pub async fn delete(self) -> ApiResult<()>

Delete this View and clean up all resources associated with it. View objects do not stop consuming resources or processing updates when they are garbage collected - you must call this method to reclaim these.

pub async fn dimensions(&self) -> ApiResult<JsValue>

Returns this View’s dimensions, row and column count, as well as those of the crate::Table from which it was derived.

• num_table_rows - The number of rows in the underlying crate::Table.
• num_table_columns - The number of columns in the underlying crate::Table (including the index column if this crate::Table was constructed with one).
• num_view_rows - The number of rows in this View. If this View has a group_by clause, num_view_rows will also include aggregated rows.
• num_view_columns - The number of columns in this View. If this View has a split_by clause, num_view_columns will include all column paths, e.g. the number of columns clause times the number of split_by groups.

pub async fn expression_schema(&self) -> ApiResult<JsValue>

The expression schema of this View, which contains only the expressions created on this View. See View::schema for details.

pub async fn get_config(&self) -> ApiResult<JsValue>

A copy of the config object passed to the Table::view method which created this View.

pub async fn get_min_max(&self, name: String) -> ApiResult<Array>

Calculates the [min, max] of the leaf nodes of a column column_name.

Returns

A tuple of [min, max], whose types are column and aggregate dependent.

pub async fn num_rows(&self) -> ApiResult<i32>

The number of aggregated rows in this View. This is affected by the “group_by” configuration parameter supplied to this view’s contructor.

Returns

The number of aggregated rows.

pub async fn schema(&self) -> ApiResult<JsValue>

The schema of this View.

The View schema differs from the schema returned by Table::schema; it may have different column names due to expressions or columns configs, or it maye have different column types due to the application og group_by and aggregates config. You can think of Table::schema as the input schema and View::schema as the output schema of a Perspective pipeline.

JavaScript Examples

const [`View`] = await table.view({ columns: ["a", "b"] });
const schema = await view.schema(); // {a: "float", b: "string"}

pub async fn to_arrow( &self, window: Option<JsViewWindow>, ) -> ApiResult<ArrayBuffer>

Serializes a View to the Apache Arrow data format.

pub async fn to_columns_string( &self, window: Option<JsViewWindow>, ) -> ApiResult<String>

Serializes this View to a string of JSON data. Useful if you want to save additional round trip serialize/deserialize cycles.

pub async fn to_columns( &self, window: Option<JsViewWindow>, ) -> ApiResult<Object>

Serializes this View to JSON data in a column-oriented format.

pub async fn to_json_string( &self, window: Option<JsViewWindow>, ) -> ApiResult<String>

Render this View as a JSON string.

pub async fn to_json(&self, window: Option<JsViewWindow>) -> ApiResult<Array>

Serializes this View to JSON data in a row-oriented format.

pub async fn to_csv(&self, window: Option<JsViewWindow>) -> ApiResult<String>

Serializes this View to CSV data in a standard format.

pub async fn on_update( &self, on_update_js: Function, options: Option<JsOnUpdateOptions>, ) -> ApiResult<u32>

Register a callback with this View. Whenever the view’s underlying table emits an update, this callback will be invoked with an object containing port_id, indicating which port the update fired on, and optionally delta, which is the new data that was updated for each cell or each row.

Arguments

• on_update - A callback function invoked on update, which receives an object with two keys: port_id, indicating which port the update was triggered on, and delta, whose value is dependent on the mode parameter.
• options - If this is provided as OnUpdateOptions { mode: Some(OnUpdateMode::Row) }, then delta is an Arrow of the updated rows. Otherwise delta will be Option::None.

Examples

// Attach an `on_update` callback
view.on_update((updated) => console.log(updated.port_id));

// `on_update` with row deltas
view.on_update((updated) => console.log(updated.delta), { mode: "row" });

pub async fn remove_update(&self, callback_id: u32) -> ApiResult<()>

Unregister a previously registered update callback with this View.

Arguments

• id - A callback id as returned by a recipricol call to View::on_update.

JavaScript Examples

const callback = () => console.log("Updated!");
const id = await view.on_update(callback);
await view.remove_update(id);

Python Examples

callback = lambda x: print(x)
cid = await view.on_update(callback)
await view.remove_update(cid)

Examples

let callback = |_| async { print!("Updated!") };
let cid = view.on_update(callback, OnUpdateOptions::default()).await?;
view.remove_update(cid).await?;

pub async fn on_delete(&self, on_delete: Function) -> ApiResult<u32>

Register a callback with this View. Whenever the View is deleted, this callback will be invoked.

Example

// attach an `on_delete` callback
view.on_delete(() => console.log("Deleted!"));

pub async fn num_columns(&self) -> ApiResult<u32>

The number of aggregated columns in this View. This is affected by the “split_by” configuration parameter supplied to this view’s contructor.

Returns

The number of aggregated columns.

pub fn remove_delete(&self, callback_id: u32) -> ApiFuture<()>

Unregister a previously registered delete callback with this View.

Example

// remove an `on_delete` callback
const callback = () => console.log("Deleted!");
view.remove_delete(callback);

pub async fn collapse(&self, row_index: u32) -> ApiResult<u32>

Collapses the row at index.

This is used during a pivot.

pub async fn expand(&self, row_index: u32) -> ApiResult<u32>

Expands the row at index.

This is used during a pivot.

pub async fn set_depth(&self, depth: u32) -> ApiResult<()>

Set expansion depth of the pivot tree.

Trait Implementations

impl Clone for View

fn clone(&self) -> View

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl From<View> for JsValue

fn from(value: View) -> Self

Converts to this type from the input type.

impl From<View> for View

fn from(value: View) -> Self

Converts to this type from the input type.

impl FromWasmAbi for View

type Abi = u32

The wasm ABI type that this converts from when coming back out from the ABI boundary.

unsafe fn from_abi(js: u32) -> Self

Recover a Self from Self::Abi.

impl IntoWasmAbi for View

type Abi = u32

The wasm ABI type that this converts into when crossing the ABI boundary.

fn into_abi(self) -> u32

Convert self into Self::Abi so that it can be sent across the wasm ABI boundary.

impl LongRefFromWasmAbi for View

type Abi = u32

Same as RefFromWasmAbi::Abi

type Anchor = Ref<'static, View>

Same as RefFromWasmAbi::Anchor

unsafe fn long_ref_from_abi(js: Self::Abi) -> Self::Anchor

Same as RefFromWasmAbi::ref_from_abi

impl OptionFromWasmAbi for View

fn is_none(abi: &Self::Abi) -> bool

Tests whether the argument is a “none” instance. If so it will be deserialized as None, and otherwise it will be passed to FromWasmAbi.

impl OptionIntoWasmAbi for View

fn none() -> Self::Abi

Returns an ABI instance indicating “none”, which JS will interpret as the None branch of this option.

impl RefFromWasmAbi for View

type Abi = u32

The wasm ABI type references to Self are recovered from.

type Anchor = Ref<'static, View>

The type that holds the reference to Self for the duration of the invocation of the function that has an &Self parameter. This is required to ensure that the lifetimes don’t persist beyond one function call, and so that they remain anonymous.

unsafe fn ref_from_abi(js: Self::Abi) -> Self::Anchor

Recover a Self::Anchor from Self::Abi.

impl RefMutFromWasmAbi for View

type Abi = u32

Same as RefFromWasmAbi::Abi

type Anchor = RefMut<'static, View>

Same as RefFromWasmAbi::Anchor

unsafe fn ref_mut_from_abi(js: Self::Abi) -> Self::Anchor

Same as RefFromWasmAbi::ref_from_abi

impl TryFromJsValue for View

type Error = JsValue

The type returned in the event of a conversion error.

fn try_from_js_value(value: JsValue) -> Result<Self, Self::Error>

Performs the conversion.

impl VectorFromWasmAbi for View

type Abi = <Box<[JsValue]> as FromWasmAbi>::Abi

unsafe fn vector_from_abi(js: Self::Abi) -> Box<[View]>

impl VectorIntoWasmAbi for View

type Abi = <Box<[JsValue]> as IntoWasmAbi>::Abi

fn vector_into_abi(vector: Box<[View]>) -> Self::Abi

impl WasmDescribe for View

fn describe()

impl WasmDescribeVector for View

fn describe_vector()