MATLAB: Add new row to String Array.

appendarrayloopsMATLABmatrixstring

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.

Best Answer

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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You are not using struct array. You are putting newdate (which is a datetime array) and full (which is a string array) into a struct strarray (see code difference below). In this case, I wonder if you just use newdate=NaT(2e6,1) and full=strings(2e6,1) directly would be faster. After all, combine these two big array into one struct won't help at all.

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s1.newdate=NaT(20,1);
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Any array must be rectangular; char() arrays are no different. The array must be as wide (have as many columns) as the longest char() string you wish it to hold and all rows must be padded to that length if they are shorter than the maximum length. You can either pre- or postpend blanks, but you can't not fill all the space with something. If you try to fool mother Matlab, you'll either get a linear string if it can interpret the comand to do so or perhaps what appears as "gibberish" if you try to place values outside the range of printing ASCII characters into a char() array as you've done above.

That's why there are cellstr() and/or strings to handle variable length strings as entities, not as just arrays of bytes of type char.

What is the end result to be made of this variable in the resulting table and why do you think a char() representation is "more better" than string() or cellstr()? Frankly, it looks like perhaps a categorical variable might be more suitable than either, but don't know the objective so can't say for certain lacking additional input.

Best Answer

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