How can I separate data by keeping the first 3 digits the same?

I have a big data file which has many variables. One of them is the userIdName ( the users name) . The first 3 digits are the same, and in the 4th digit the userIdName changes, for example 1001001,1001002,1001003 belong to the same userid , but 1002001 is a different userIdName. I have almost 100000 of those numbers and I want to find how many userIdNames I have. How can I do that? Shall I use For Loop?

[David Goodmanson]

Hello Katrin,

you may or may not have to use a for loop to extract the data, but the best approach is to get the useridnames into one column in the Matlab workspace.

For any positive integer n you can use fix(n/10^d) to lop off d digits, and that command works on an array of such numbers. Then take a look at the 'unique' function.

[Star Strider]

What are the ‘userIdName’ values?

Numeric, or character-array variables or something else?

[Katrin Kamp]

numeric variables

[Katrin Kamp]

https://www.mathworks.com/matlabcentral/answers/364120-how-can-i-separate-data-by-keeping-the-first-3-digits-the-same#comment_498991

thank you very much!!! it was a very helpful answer!