# Finding a way to iterate using the input of two xarray dataarrays when chunked

**URL:** https://forum.access-hive.org.au/t/finding-a-way-to-iterate-using-the-input-of-two-xarray-dataarrays-when-chunked/4018
**Category:** Technical
**Tags:** help
**Created:** [20 December 2024 02:05 UTC](https://forum.access-hive.org.au/t/finding-a-way-to-iterate-using-the-input-of-two-xarray-dataarrays-when-chunked/4018 "2024-12-20T02:05:03Z")
**Posts on this page:** 1
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### Author: ![rogierw](https://avatars.discourse-cdn.com/v4/letter/r/53a042/32.png) [@rogierw](https://forum.access-hive.org.au/u/rogierw)
#### Post date: [13 January 2025 00:30 UTC](https://forum.access-hive.org.au/t/finding-a-way-to-iterate-using-the-input-of-two-xarray-dataarrays-when-chunked/4018/4 "2025-01-13T00:30:19Z")

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Thank Anton and Jemma,  
Those are excellent responses. However, I do not think I can use cumsum. It is because I did not explain well enough in my initial example. So entirely my fault.

After the summing of storage a bunch of conditions need to be met, such as the value of arr\_storage not being able to be larger than my\_max (see below). Hence, the cumsum solution is too simple.

```auto
da = xr.DataArray(
    np.random.randint(low=-5, high=5, size=(10, 100, 100)),
    coords=[range(10), range(100), range(100)],
    dims=["time", "x", "y"],
).chunk(chunks={"x":10, "y":10})

my_max = 10
def sum_storage(arr):
    arr_storage = xr.zeros_like(arr)
    for idx in range(1,len(arr)):
        # print(f'idx: {idx}')
        arr_storage[dict(time=idx)] = arr_storage[dict(time=idx-1)] + da[dict(time=idx)]
        arr_storage[dict(time=idx)] = arr_storage[dict(time=idx)].where(arr_storage[dict(time=idx)] <= my_max, my_max)
    return arr_storage

%time arr_storage = sum_storage(da)

```

I am now thinking of a solution of manually chunking the parts when they outgrow memory. But that does not sound ideal, i.e. I don’t want to write a lot of manual code when a possible chunked solution is also available…

Thanks for your time, hope you can look at it again?

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