Determine if an element in array of doubles start with patten

Question

Mohamed Asaad 2023-2-12

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1911285-determine-if-an-element-in-array-of-doubles-start-with-patten

评论： Adam Danz 2023-2-12

Screenshot 2023-02-12 214423.png

Hey,

I need to find the index of the first element that starts with a specific number. So in this picture for example, if i give 8 as an input, i want the code to give me back the index of the first 8. that it meets which would be 163 in this case.

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Answer 1

Voss 2023-2-12

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https://ww2.mathworks.cn/matlabcentral/answers/1911285-determine-if-an-element-in-array-of-doubles-start-with-patten#answer_1169925

在 MATLAB Online 中打开

idx = find(floor(data)==val,1)

where data is your array and val is what you're looking for, e.g., 8.

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Adam Danz 2023-2-12

Neither of our current answers work with negative values although that may not be a problem in the OP's use case.

The benefit of this answer over mine is that val can be any number of digits. You could search for "82" in an array of values. It would match the third element of [8.2 820 82 8200].

The benefit of my answer over this one is that only the first digit is considered in the search but is limited to single-digit target values (which could easily by adapted). You could search for the number 8 in this vector and it would match the 3rd element. [0.8, 18, 8203, 8, 80].

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Answer 2

Adam Danz 2023-2-12

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1911285-determine-if-an-element-in-array-of-doubles-start-with-patten#answer_1169930

编辑：Adam Danz 2023-2-12

在 MATLAB Online 中打开

Here's a demo that finds the first value in a vector that has a first digit equal to 4. The values can have any number of digits to the left of the decimal although this doesn't work with negative values.

rng default
val = sort(rand(1,10).*randi(500,1,10))'
val = 10×1
    6.9254
   58.7631
   60.8267
   64.3632
  221.9503
  250.4717
  253.5761
  380.1302
  440.2149
  463.1465
target = 4; 
firstDigit = cellfun(@(v)v(1),""+val)-'0'
firstDigit = 10×1
     6
     5
     6
     6
     2
     2
     2
     3
     4
     4
firstDigitIdx = find(firstDigit == target,1,'first')
firstDigitIdx = 9