# Select and Calculate

A WireBootstrap [DataTable](/wirebootstrap/reference/wire.data/wire.data.datatable.md) allows rows of data to be selected, aggregated, and transformed. 

## Select

The following example selects two columns, `product` and `price`, from the data table and creates a new data table using the `table` function at the end of the method chain.

```javascript
let data = [ 
    { product: "apples", order: "PRN001", quantity: 10, price: 5.5 },
    { product: "oranges", order: "PRN002", quantity: 15, price: 6 },
    { product: "bananas", order: "PRN002", quantity: 20, price: 7.5 }
];

let table = new wire.data.DataTable(data);
 
table = table.select("product", "price").table();
```

## Format

Columns have a  number of attributes that can be set in the `select` method chain.  In order to set these attributes, reference an individual column using the `column` method and then use any number of the [column](/wirebootstrap/reference/wire.data/wire.data.datatable/columns.md) attribute methods to set it's values.

Use the `as` function to change the name of a field.  In the example below, the field `quantity` will be named `number_of_skus` in the new table.

```javascript
...

table = table.select().column("quantity").as("number_of_skus").table();
```

### Title

Use the `title` function to give any column a descriptive title. This will be set into the `Title` property for the column in the resulting table.

```javascript
...

table = table.select().column("product").title("Product Title").table();
```

A data table needs a descriptive `Title` value for any column.  If one is not supplied, it will automatically create one.  In doing so, it will parse *camelCase* or *PascalCase* field names and intelligently capitalize and space accordingly to come up with a friendly title.

In the example below, a title for the `numberOfSkus` column is not supplied.  In the new table, the title will automatically be `Number Of Skus`.

```javascript
...

table = table.select().column("quantity").as("numberOfSkus").table();
```

### Number Formatting

To format numeric columns, use the format method with a format specification.  Valid values are *C\[N]*, *P\[N]*, *N\[N]* where *\[N]* is the number of decimal places.

The example below sets the formatting for the `price` column to currency one decimal place using the `C1` parameter in the `format` function.  This value will be set into the `Format` property for the column in the resulting table.

```javascript
...

table = table.select("product").column("price").format("C1").table();
```

### Custom Formatting

The format method can also accept a custom function in order to format data in the column.  

The following example formats a date field called `date_field` using the third party library [moment.js](https://momentjs.com).

```javascript
...

table = table.select().column("date_field").format((row) => {
    return moment(row["date_field"]).format("MM-DD-YYY");
}).table();
```

## Calculated Columns

Data tables allow calculated columns to be created on the fly.

The following creates two columns in a new data table that are the aggregates of columns in an existing data table.  In the new table, `quantity` will be aggregated using `sum`.  It will have the same name and be formatted to numeric one decimal place using `format` `N1`.  The `price` column will be averaged using `avg` and it's name changed to `avg_price`.  It will be formatted to currency one decimal place using `format` `C1`.

```javascript
...

table = table.select()
    .sum("quantity").format("N1")
    .avg("price").as("avg_price").format("C1")
    .table();
```

Aggregates can also be used with implicit grouping by selecting other columns to be included in the result. In the example below, the `order` column is included in the new data table, so the calculated column `quantity` is broken out by `order`.

```javascript
...

table = table.select("order").sum("quantity").table();
```

 Calculated columns can also be created using custom formulas using the `calc` method.

In the example below, a new column, `more_quantity`, is calculated as the `sum` of the `quantity` column times `10` and returned in a new table.  This is done using a custom function and a delegate `row`.  The function will also have the index position and all rows in the data table available as it is being evaluated.

```javascript
...

table = table.select()
    .column("more_quantity")
    .sum().calc((row, index, rows) => {
        return row["quantity"] * 10;
    })    .table();
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.wirebootstrap.com/wirebootstrap/working-with-datatables/select-and-calculate.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.