# How to scan data on a key?

**URL:** <https://forum.cloverdx.com/t/how-to-scan-data-on-a-key/715>\
**Category:** CloverDX Platform\
**Created:** [May 28, 2010, 12:00am UTC](https://forum.cloverdx.com/t/how-to-scan-data-on-a-key/715 "2010-05-28T00:00:00Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![avackova](https://avatars.discourse-cdn.com/v4/letter/a/65b543/32.png) [@avackova](https://forum.cloverdx.com/u/avackova)\
**Post date:** [May 28, 2010, 12:00am UTC](https://forum.cloverdx.com/t/how-to-scan-data-on-a-key/715/1 "2010-05-28T00:00:00Z")

</div>

What component would I use if I wanted to scan a sorted input dataset on a key to generate a running total or some implicit grouping of records?

Here’s an example:  
K: the key that can be based on one or more fields  
D: some data  
S: data indicator for switching the key context  
G: a grouping based on the key and “seeing” the switch

I may have the following dataset:

```auto

K1 D1
K1 D2
K1 S
K1 D3
K1 D4
K1 D5
K1 S
K2 D1
K2 S
K2 D2
K2 D3
K2 S

```

I might want to create a running counter or group them together by creating  
the latter two fields:

```auto

K1 D1 1 G1
K1 D2 2 G1
K1 S 3 G1
K1 D3 1 G2
K1 D4 2 G2
K1 D5 3 G2
K1 S 4 G2
...

```

---

<div class="post-metadata">

**Author:** ![avackova](https://avatars.discourse-cdn.com/v4/letter/a/65b543/32.png) [@avackova](https://forum.cloverdx.com/u/avackova)\
**Post date:** [May 28, 2010, 11:34am UTC](https://forum.cloverdx.com/t/how-to-scan-data-on-a-key/715/2 "2010-05-28T11:34:03Z")

</div>

To achieve this aim, you need to use [Rollup](http://wiki.cloveretl.org/doku.php?id=components:transformers#rollup) component with following code:

```auto

//#TL
string SWITCH_VALUE = "S";

int count;
int groupCount = 0;
boolean wasSwitch;
// Called for the first data record in a new group. Starts the parsing of the new group.
function initGroup(groupAccumulator) {
	count = 0;
	groupCount++;
	wasSwitch = false;
}

// Called for each data record in the group (including the first one and the last one).
// Implicitly returns false => updateTransform() is not called. When returns true, calls updateTransform().
function updateGroup(groupAccumulator) {
	if (wasSwitch) {//next group
		count = 1;
		groupCount++;
		wasSwitch = false;
	}else{//group continues
		count++;
		if ($value == SWITCH_VALUE) {//indicator for switching the key context found
			wasSwitch = true;
		}
	}
	return true;//we need to call updateTransform function
}

// Called to transform data records that have been parsed so far into user-specified number of output data record(s).
// Counter (incremented by 1 starting from 0) stores the number of previous calls to this method for the current group update.
// Group accumulator can optionally be used.
// Function implicitly returns SKIP to skip sending any data records to output.
// Returning ALL causes each data record to be sent to all output port(s).
// Can also return a number of the output port to which individual data record should be sent.
function updateTransform(counter, groupAccumulator) {
	if (counter > 0) return SKIP;//call this function once only for each input record
	$key := $key; //mapping of input field
	$value := $value; //mapping of input field
	$counter := count; //create additional information
	$groupping := "G" + groupCount; //create additional information
	return ALL //by default the function returns SKIP, so we need to inform the component to send record on output port
}

// Called for the last data records in all groups sequentially, but only after all incoming data records have been parsed.
// Implicitly returns true => transform() is called for the whole group.
function finishGroup(groupAccumulator) {
	return false;//we have transformed and sent to output all records in updateTransform function
}

// Called to transform the whole group of incoming data record(s) into user-specified number of output data record(s).
// Counter (incremented by 1 starting from 0) stores the number of previous calls to this method for the current group update.
// Group accumulator can optionally be used.
// Function implicitly returns SKIP to skip sending any data records to output.
// Returning ALL causes each data record to be sent to all output port(s).
// Can also return a number of the output port to which individual data record should be sent.
function transform(counter, groupAccumulator) {
   //this function is never called as finishGroup returns false
}

```

The above implementation doesn’t use group accumulator at all. Following implementation does the same , but with group accumulator usage:

```auto
//#TL
string SWITCH_VALUE = "S";

int count;
int groupCount = 0;
boolean wasSwitch;
// Called for the first data record in a new group. Starts the parsing of the new group.
function initGroup(groupAccumulator) {
	groupCount++;
	wasSwitch = false;
	groupAccumulator["counter"] = 0;
	groupAccumulator["groupping"] = "G" + groupCount;
}

// Called for each data record in the group (including the first one and the last one).
// Implicitly returns false => updateTransform() is not called. When returns true, calls updateTransform().
function updateGroup(groupAccumulator) {
	if (wasSwitch) {
		groupAccumulator["counter"] = 1;
		groupCount++;
		groupAccumulator["groupping"] = "G" + groupCount;
		wasSwitch = false;
	}else{
		groupAccumulator["counter"] = groupAccumulator["counter"] + 1;
		if ($value == SWITCH_VALUE) {
			wasSwitch = true;
		}
	}
	return true;
}

// Called for the last data records in all groups sequentially, but only after all incoming data records have been parsed.
// Implicitly returns true => transform() is called for the whole group.
function finishGroup(groupAccumulator) {
	return false;
}

// Called to transform data records that have been parsed so far into user-specified number of output data record(s).
// Counter (incremented by 1 starting from 0) stores the number of previous calls to this method for the current group update.
// Group accumulator can optionally be used.
// Function implicitly returns SKIP to skip sending any data records to output.
// Returning ALL causes each data record to be sent to all output port(s).
// Can also return a number of the output port to which individual data record should be sent.
function updateTransform(counter, groupAccumulator) {
	if (counter > 0) return SKIP;
	$key := $key;
	$value := $value;
	$counter := groupAccumulator["counter"];
	$groupping := groupAccumulator["groupping"];
	return ALL
}

// Called to transform the whole group of incoming data record(s) into user-specified number of output data record(s).
// Counter (incremented by 1 starting from 0) stores the number of previous calls to this method for the current group update.
// Group accumulator can optionally be used.
// Function implicitly returns SKIP to skip sending any data records to output.
// Returning ALL causes each data record to be sent to all output port(s).
// Can also return a number of the output port to which individual data record should be sent.
function transform(counter, groupAccumulator) {
}
 }

```