---
title: "FirstDiscreteByIndex"
slug: "firstdiscretebyindex"
updated: 2022-02-10T19:26:37Z
published: 2022-02-10T19:26:37Z
canonical: "docs.datajet.app/firstdiscretebyindex"
---

> ## Documentation Index
> Fetch the complete documentation index at: https://docs.datajet.app/llms.txt
> Use this file to discover all available pages before exploring further.

# FirstDiscreteByIndex

## General: FirstDiscreteByIndex

## Creates a flag field where the first occurrence of each unique value in the specified field is set to 1 – but derived as if the table is in order of the sort field

## Purpose

Use this function to:

- Sort Data by a specified field before flagging the first unique value
- Flag earliest record

## Return Value

| Property | Value |
| --- | --- |
| **FieldType** | Integer |
| **FieldSize** | Low |
| **DataType** | Discrete |
| **DataSize** | Byte |

```shell
Example Return Value: 0 , 1, null
```

![](https://cdn.document360.io/73b6469b-c1e4-47e9-aa65-986c8ebd17ca/Images/Documentation/Gen_FDByIndex_Sample.PNG)

## Parameters

| Parameter | JSON | Description |
| --- | --- | --- |
| **Table** | “targetTable”: “MyTableName” | The target table on which the new field will be created |
| **Filter** | “dataset”: {DataSet_JSON} | Optional. If a filter is applied, records not in the filter recordset will be returned as null. |
| **Function** | "function":"" |  |
| **Distinct Key** | “p1”: “” | Required. Once the data has been “sorted” by the **Sort Field**, the *first occurrence* of each unique value of Distinct Key will be flagged. Must be a Discrete DataType from the target table - will not work with continuous fields. Continuous Fields If a continuous field needs to be used, it may be possible to derive a discrete field from the continuous field using the CONCAT function. It may be necessary to apply a filter to reduce the number of discrete values. |
| **Sort Field** | “p2”: | Required. Field used to determine the sort order of the Recordset. The first occurrence of **Distinct Key** in the sorted Recordset will be flagged. Must be a discrete DataType from the target table. Will not work with continuous fields. |

## JSON Sample

```json
{
  "method": "BuildBakedField",
  "project": "D3",
  "targetTable": "transactions",
  "overwrite": true,
  "name": "FD_Product_ByDate",
  "function": "firstdiscretebyindex",
  "p1": "product",
  "p2": "date"
}
```

## Usage Notes

![](https://cdn.document360.io/73b6469b-c1e4-47e9-aa65-986c8ebd17ca/Images/Documentation/Gen_FDByIndex_Usage.png)

If no filter is applied, the number of “1’s” in FirstDiscreteByIndex will match the number of unique values in the Recordset for the specified DistinctKey. (By default the Recordset is all records in the target table)

![](https://cdn.document360.io/73b6469b-c1e4-47e9-aa65-986c8ebd17ca/Images/Documentation/Gen_FDByIndex_Usage1.png)

See Also:

- Engineering | Expression Field
- FirstDiscrete  (General Functions)

## Example

| Example | Details |
| --- | --- |
| **Description** | **Flag earliest product record for year 2020** |
| **Input** | - Table: = [transactions] - Filter: = {[transactions].[year]=2020} - **Function: = FirstDiscreteByIndex** - Distinct Key:= product - Sort Field:= date - Name: =FD_Product_ByDate_2020 |
| **Sample** | ![](https://cdn.document360.io/73b6469b-c1e4-47e9-aa65-986c8ebd17ca/Images/Documentation/Gen_FDByIndex_Example.png) |