---
title: "system.tag.queryTagDensity"
description: "Queries the Tag history system for information about the density of data."
---

# system.tag.queryTagDensity

> Queries the Tag history system for information about the density of data.

This function is used in **Python Scripting**.

## Description
Queries the Tag history system for information about the density of data. In other words, how much data is available for a given time span. 

This function is called with a list of Tag paths, and a start and end date. The result set is a two column dataset specifying the timestamp, and a relative weight. Each row is valid from the given time until the next row. Tags are assigned a 1 or a 0 if they are present or not. All values are then multiplied together to get a decimal based percentage for the density. Thus, for four Tag paths passed in, if three Tags were present during the span, the result would be 0.75.

## Client Permission Restrictions
This scripting function has no [Client Permission](projects\project-properties\project-properties.md#client---permissions) restrictions.

## Syntax
`system.tag.queryTagDensity(paths, startDate, endDate)`

### Parameters

| Type | Parameter | Description |
|---|---|---|
| PySequence | `paths` | An array of Tag paths (strings) to query. |
| Date | `startDate` | The start of the range to query. |
| Date | `endDate` | The end of the range to query. |

### Returns
**Dataset** - A 2-column dataset consisting of a timestamp and a weight. Each row is valid until the next row.

### Scope
All

## Code Examples
```python title="Example #1"
# Will grab the density of a tag and print it out to the console.
density = system.tag.queryTagDensity(
    ['[default]myTag'],
    system.date.addHours(system.date.now(), -24),
    system.date.now())  
 
density = system.dataset.toPyDataSet(density)
for row in density:
    print row[0], row[1]
```

```python title="Example #2"
# Create a list of times going back in time at day increments.
# This forces density readouts at each day, even if two days had the same density
now = system.date.now()
times = [system.date.addDays(now, -1), system.date.addDays(now, -2), system.date.addDays(now, -3), system.date.addDays(now, -4), system.date.addDays(now, -5), system.date.addDays(now, -6)]
 
# Create start and end date variables, as well as a variable that holds each history density.
startDate = now
endDate = now
list = []
 
# Loop through the list of times
for time in times:
 
    # Set the new end date to whatever the start date was previously
    # and the new start date to the next time in the list.
    endDate = startDate
    startDate = time
     
    # Query Tag Density using a list of Tagpaths with the startDate and endDate values.
    density = system.tag.queryTagDensity(
    ['[default]tag1', '[default]tag2', '[default]tag3', '[default]tag4', '[default]tag5'],
    startDate, endDate)
     
    # Add each row of the returned dataset to a list of rows.
    density = system.dataset.toPyDataSet(density)
    for row in density:
        list.append([row[0], row[1]])
         
# Place the results in a table.
event.source.parent.getComponent('Table').data = system.dataset.toDataSet(['Times', 'Density Percentages'], list)
```

```python title="Example #3"
# Create a list of times going back in time at day increments.
# This forces density readouts at each day, even if two days had the same density.
# This differs from the previous example in that it uses the new system.dataset.appendDataset function, which is only available in 7.9.7.
now = system.date.now()
times = [system.date.addDays(now, -1), system.date.addDays(now, -2), system.date.addDays(now, -3), system.date.addDays(now, -4), system.date.addDays(now, -5), system.date.addDays(now, -6)]
 
# Create start and end date variables.
startDate = now
endDate = now
 
# Loop through the list of times.
for time in times:
    # Set the new end date to whatever the start date was previously
    # and the new start date to the next time in the list.
    endDate = startDate
    startDate = time
     
    # Query Tag Density using a list of Tagpaths with the startDate and endDate values.
    density = system.tag.queryTagDensity(
    ['[default]EquipmentFour', '[default]Ramp/Ramp6', '[default]Ramp/Ramp7', '[default]Ramp/Ramp8', '[default]Ramp/Ramp9'],
    startDate, endDate)
    if endDate == now:
        densities = density
    else:
        densities = system.dataset.appendDataset(densities, density)
     
# Place the results in a table.
event.source.parent.getComponent('Table').data = densities
```