# extendData for dcc.Graph subplots

**URL:** <https://community.plotly.com/t/extenddata-for-dcc-graph-subplots/51413>\
**Category:** Dash Python\
**Created:** [March 25, 2021, 8:35pm UTC](https://community.plotly.com/t/extenddata-for-dcc-graph-subplots/51413 "2021-03-25T20:35:52Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![nsbruce](https://avatars.discourse-cdn.com/v4/letter/n/96bed5/32.png) [@nsbruce](https://community.plotly.com/u/nsbruce)\
**Post date:** [March 25, 2021, 8:35pm UTC](https://community.plotly.com/t/extenddata-for-dcc-graph-subplots/51413/1 "2021-03-25T20:35:52Z")

</div>

I have a Dash app with a `dcc.Graph()` component. The component has subplots which I would like to update using a callback. The first subplot is a line plot while the second is a heatmap. I need to update the y values in the first and the z values in the second.

The figure is set with:

```auto
dcc.Graph(id='spec-waterfall', responsive=True, figure={
    'data': [
        {
            'type': 'line',
            'xaxis': 'x1',
            'yaxis': 'y1',
            'y': spec[0],
        },
        {
            'type': 'heatmap',
            'xaxis': 'x1',
            'yaxis': 'y2',
            'z': spec,
        }
    ],
    'layout': {
        'xaxis1': {
            'anchor': 'y1',
            'domain': [0.0, 1.0],
        },
        'yaxis1':{
            'anchor': 'free',
            'domain': [0.65, 1.0],
            'position': 0.0,
        },
        'yaxis2': {
            'anchor': 'x1',
            'domain': [0.0, 0.55],
        }
    }
})

```

Where `spec` is a 2D array. I attempt to update it in a callback with the `extendData` property since I don’t want to replace the entire figure each time (a lot of data has to be processed - it is preferable to only replace the data instead of the entire figure).

```auto
@app.callback(
    [Output("spec-waterfall", "extendData")],
    [Input("my-interval-timer", "n_intervals")],
    prevent_initial_call=True
)
def update_fig(index,spec=spec):
    newLine = # build 1D array of y values for line plot
    newSpec = # build 2D array of z values for heatmap

    updatedData = [dict(y=[newLine], z=[newSpec]), [0,0], [len(newLine), len(newSpec)]]
    return updatedData

```

But this errors out with the `extendData` arguments having the wrong shape. Any tips are appreciated!