why is 'gather' performance dramatically poor when I evaluate a tall array (105151 Bytes) by an indexing operation

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Eva-Maria Weiss
Eva-Maria Weiss 2019-7-19
编辑： Eva-Maria Weiss 2019-7-22
Hi experts,
I have a tall array from type double (Mx386) containing voltage values in each .
For visualization purposes I want to evaluate the first values of one electrode, but this single process took 5 h.
test1 = gather(test(1:500,3));
Also evaluating the tall array to get size is a time consumpting events
gather(size(test,1))
How can I accelerate the process? What could likely be the issue?
I'm happy about any hint to solve this.
Thank you in advance!
Eva
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Eva-Maria Weiss
Eva-Maria Weiss 2019-7-22
编辑：Eva-Maria Weiss 2019-7-22
Yes, know I get it. Sorry, I'm from biological field, and try to step into data analysis right now. So underlying computer processes are not always clear to me, that means hints like
when you gather like that, it forces matlab to go through reading all columns of the array (in batches of rows) and extract the used columns from that
are super helpful for me. I didn't know that before.
I'll try out transformedDatastore now, to apply the filter function. instead of using the creation of a tall array at this place.
Thanks for your help!

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