How to extract digits

a = [438;259;21;44;79876];
power10 = 10.^floor(log10(a));
first_digit = floor(a./power10)
first_digit = 5×1
     4
     2
     2
     4
     7
first_two_digits = floor(a./power10*10)
first_two_digits = 5×1
    43
    25
    21
    44
    79

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Voss 2022-3-25

在 MATLAB Online 中打开

That is indeed an array of characters (in particular, it is a character vector - a vector being a 1-dimensional array; in this case it is a row vector, i.e., of size 1-by-something).

Here's how you could extract the first digit (or first two digits) of each number in there, resulting in a cell array of character vectors or a character array.

(The idea is to read the character vector ST using sscanf() to get numbers and then use the approach in my answer to get the numeric digit(s), then 'print' those digit(s) to into a cell array or character array using sprintfc() or sprintf().)

ST = '51         51         50        49         49';
a = abs(sscanf(ST,'%f'))
a = 5×1
    51
    51
    50
    49
    49
power10 = 10.^floor(log10(a));
first_digit = sprintfc('%d',floor(a./power10))
first_digit = 5×1 cell array
    {'5'}
    {'5'}
    {'5'}
    {'4'}
    {'4'}
first_two_digits = sprintfc('%d',floor(a./power10*10))
first_two_digits = 5×1 cell array
    {'51'}
    {'51'}
    {'50'}
    {'49'}
    {'49'}

Those are the cell array results, and here's the character array version (with one or two columns depending on if you're taking one or two digits):

first_digit = sprintf('%d',floor(a./power10)).'
first_digit = 5×1 char array
    '5'
    '5'
    '5'
    '4'
    '4'
first_two_digits = reshape(sprintf('%d',floor(a./power10*10)),2,[]).'
first_two_digits = 5×2 char array
    '51'
    '51'
    '50'
    '49'
    '49'

Now, let's say ST was like this instead:

ST = '-5.1 +5.1e+002 50.0 -49e-3 49';

Then the approach above will still work:

a = abs(sscanf(ST,'%f'))
a = 5×1
    5.1000
  510.0000
   50.0000
    0.0490
   49.0000
power10 = 10.^floor(log10(a));
first_digit = sprintfc('%d',floor(a./power10))
first_digit = 5×1 cell array
    {'5'}
    {'5'}
    {'5'}
    {'4'}
    {'4'}
first_two_digits = sprintfc('%d',floor(a./power10*10))
first_two_digits = 5×1 cell array
    {'51'}
    {'51'}
    {'50'}
    {'49'}
    {'49'}
first_digit = sprintf('%d',floor(a./power10)).'
first_digit = 5×1 char array
    '5'
    '5'
    '5'
    '4'
    '4'
first_two_digits = reshape(sprintf('%d',floor(a./power10*10)),2,[]).'
first_two_digits = 5×2 char array
    '51'
    '51'
    '50'
    '49'
    '49'

But let me reiterate that this approach still has the limitation that the two-digit result for a one-digit number will not be accurate ('4' will return '40' for instance).

In general, the best choice of method will depend on:

what format(s) the numbers in the ST character vector might possibly be in, and
what class of variable you want to end up with, e.g., cell array of character vectors, character array, string array, numeric array

Stephen23 2022-3-25

在 MATLAB Online 中打开

ST = '51         51         50        49         49';
DD = regexp(ST,'\d\d','match')
DD = 1×5 cell array
    {'51'}    {'51'}    {'50'}    {'49'}    {'49'}

LC 2022-3-26

thank you very much for your support, it works great because I never have a one-digit number.

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How to extract digits

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