# Issue with Assigning Values to Sub-Epochs in MNE Epochs Object
**URL:** https://mne.discourse.group/t/issue-with-assigning-values-to-sub-epochs-in-mne-epochs-object/10718
**Category:** Support & Discussions
**Tags:** eeg, epochs
**Created:** [January 19, 2025, 5:47am UTC](https://mne.discourse.group/t/issue-with-assigning-values-to-sub-epochs-in-mne-epochs-object/10718 "2025-01-19T05:47:27Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@Jianyang](https://mne.discourse.group/u/Jianyang)
#### Post date: [January 19, 2025, 5:47am UTC](https://mne.discourse.group/t/issue-with-assigning-values-to-sub-epochs-in-mne-epochs-object/10718/1 "2025-01-19T05:47:27Z")
Dear MNE Experts,
I am working with an `EpochsArray` object that contains different `event_id` categories. However, I encountered an issue when trying to apply a z-score transformation to the data corresponding to each specific `event_id`. Below is a description of the problem:
### **Epoch Structure**
```python
```
### **Working Example**
When applying a moving average transformation across all data in the `EpochsArray`, it works perfectly:
```python
for i_shape1 in range(epoch._data.shape[0]):
epoch._data[i_shape1,:,:] = JY_basic_func.moving_average(epoch._data[i_shape1,:,:] , np.ones(window) / window)
```
### **Problematic Code**
However, when I attempt to apply a z-score transformation to each `event_id` subset using the following code, the data inside `epoch[i_key]._data` does not update:
```python
for i_key in epoch.event_id.keys():
if z_type =='channel':
epoch[i_key]._data = zscore(epoch[i_key]._data,axis=1)
```
After running this, `epoch[i_key]._data` remains unchanged.
### **Question**
Is there a convenient way to modify the data corresponding to each `event_id` within an `EpochsArray` structure? Any suggestions or guidance would be greatly appreciated.
#### System Information:
- MNE version: e.g. 1.5.1
- operating system: e.g. Windows 10
Thank you for your time and support!
Best regards,
Jianyang
---
### Author:  [@richard](https://mne.discourse.group/u/richard)
#### Post date: [January 19, 2025, 9:18pm UTC](https://mne.discourse.group/t/issue-with-assigning-values-to-sub-epochs-in-mne-epochs-object/10718/2 "2025-01-19T21:18:33Z")
Hello!
> [@Jianyang](#):
>
> However, when I attempt to apply a z-score transformation to each `event_id` subset using the following code, the data inside `epoch[i_key]._data` does not update:
I believe indexing `Epochs` creates a copy, so you’re modifying a copy and immediately discarding it … I don’t know from the top of my head how you could solve this, but I suppose you could build something with the help of [`Epochs.apply_function()`](https://mne.tools/stable/generated/mne.Epochs.html#mne.Epochs.apply_function) and take care of the different event types inside the function you call (you’d need to pass the events array for this).
Good luck,
Richard
---
### Author:  [@Jianyang](https://mne.discourse.group/u/Jianyang)
#### Post date: [January 20, 2025, 11:42am UTC](https://mne.discourse.group/t/issue-with-assigning-values-to-sub-epochs-in-mne-epochs-object/10718/3 "2025-01-20T11:42:37Z")
Get it. Now I have created a dictionary to store the z-score data. Thank you very much.
---
### Author:  [@system](https://mne.discourse.group/u/system)
#### Post date: [January 27, 2025, 11:43am UTC](https://mne.discourse.group/t/issue-with-assigning-values-to-sub-epochs-in-mne-epochs-object/10718/4 "2025-01-27T11:43:10Z")
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