Add new row to String Array.

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Adam Brabec 2020-7-12

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评论： Adam Brabec 2020-7-19

采纳的回答： the cyclist

Hi,

I have a Xx1 string array and I currently have something on the lines of:

strarray.full = [strarray.full;NEWDATA];

The code will add a new line each loop, and will re create the string array each time.

This works fine for smaller files, but the txt files I am reading are around 200,000 lines, so this takes around 20 minutes to run.

I am trying to get something like this to work to avoid having to re create the matrix each loop and make it alot faster.

strarray.full(end+1,1) = NEWDATA

I keep getting the Error "Unable to perform assignment becuse the indices on the left side are not compatible with the size of the right side"

The first loop results in an empty NEWDATA. I also do not believe I am allowed to share the code itself.

Thanks.

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the cyclist 2020-7-12

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https://ww2.mathworks.cn/matlabcentral/answers/563849-add-new-row-to-string-array#answer_464804

You can preallocate memory for the entire string array with

str = strings(200000,1);

and then fill row-by-row rather than appending. This will avoid the string array being copied to different memory locations as it fills, and should radically speed up the operation.

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Adam Brabec 2020-7-12

编辑：Adam Brabec 2020-7-12

Hi Cyclist,

I was able to rework the code in the way you suggested so thank you.I'm not sure why, but it appears to be slower than the original method.

The loop times still drastically increase as the matrix is being filled. I stopped it at around 30 minutes.

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Adam Brabec 2020-7-13

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I was able to find a fix using a "Dumping matrix" that after each .txt file I read, it takes the dump matrix and add it to the end larger matrix.

This knocked the time down from 20 minutes to 7 minutes.

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the cyclist 2020-7-18

Not frustrated, and I don't feel like I wasted my time. I'm just trying to help you get to a solution efficiently.

Just bear in mind that any work you leave for someone else, rather than doing that prep work yourself, has to be done by every person who tries to help you. So, it can be a hurdle that some people just won't bother with.

Adam Brabec 2020-7-19