Extracting number from a string

How can I extract the number 1 from the string 'M1' ?

Answer 1

[Stephen23]

Here are two very simple methods:

>> str = 'M1';
>> sscanf(str,'M%d')
ans =  1
>> str(2)-'0'
ans =  1

[Anh Tran]

Thanks for the great answer! But can you also explain the code for me?

[Stephen23]

sscanf reads the numeric values in a string. Read its documentation to know how it works.

The second method subtracts the character code for the character '0' from the second character of the string. This is a simple way of converting digits into a vector of values.

Answer 2

[José-Luis]

result = 'M1' - '0';
result(result < 0 | result > 9) = [];

[Anh Tran]

Thanks for the great answer! But can you also explain the code for me?

Answer 3

[Image Analyst]

Here are two ways, depending on if you want the extracted "1" to be a character (string) or a number:

str = 'M1' % First define the string.
str1 = str(2) % Gives a character
dbl1 = str2double(str(2))  % Give a number (double)

[Anh Tran]

Thanks! That's a great explanation.

Answer 4

[Pierre Harouimi]

You can use pattern from R2020b:

numbers = str2double(extract(string, digitsPattern));

[Image Analyst]

Example:

string = 'abc123def456789ghi'

string = 'abc123def456789ghi'

numbers = str2double(extract(string, digitsPattern))

numbers = 2×1

123 456789

It would be nice if they made a little wrapper function for that, since it's hard to remember. Something simple like

numbers = extractNumbers(string);

would be easier for most people I think, than having to know about digitsPattern, extract, str2double, and then having to nest them all together.

[Stephen23]

"Something simple like... would be easier for most people I think..."

The devil is in the details, because it really depends on what you define as a "number". Some users will want to match fractional digits (which probably means selecting for e.g. comma vs dot vs comma|dot), whereas others will want to match only integers and to treat commas/dots as non-numeric. Ditto exponent notation, NaNs, Infs, other bases, fixed-width numbers, various Unicode minus/plus signs, etc.

So it turns out to be not very simple at all, once the different "number" formats are considered. The user specifying a regular expression or MATLAB pattern is one way to give them that control, by making those choices explicit.