i need help replacing the integers in this file.

I have a function replaceMultiples that I am trying to write. it is supposed to take an input as a filename (fname) of a text file, and a natural number (num). Where each line of the text file contains one or more integers, separated by a blank space. Go through the text file fname line by line and replaces each integer that is a multiple of num by the integer divided by num. And write the modified text file to a text file with the same name as the original file, but started with ’updated# ’, where # represents the number num. I need it to also display the number of integers that were replaced. For example, if I have a file:

example.txt

123 571 −33 

14 15 18

6 9 

28 25 33 3

An example input:

n=replaceMultiples(’example.txt’,3)  %the value of "n" should equal 8 (the number of integers replaced)

After executing the script the command window should show n=8 and

the new file would appear as "updated3 example.txt " and look like this:

41 571 −11 
14 5 6 
2 3 
28 25 11 12

I have this script written so far, but have some problems with it I cannot figure out.

function numReplaced =replaceMultiples(fname, num)
ifh=open(fname,'r');  %open the input file for reading
ofn = sprintf('%s%d%s', 'updated_', num, fname); %creates the output file name
ofn=fopen(ofn, 'wt')     %open the output file for writing
numReplaced=n;
n=0;
ln=' ';  %initiation of ln
while isnumeric(fname)
    ln=fgetl(ifh);
    if isnumeric(ln)
        while ~isempty(ln)

              if strcmp(tk/num=1) %calls integers divisable by num
                  fprint(ofh,' %s',tk); %write it to the input file
              end
              fprintf9ofh,'\n');
          end
      end
  end
  flcose(ifh);
  fclose(ofh);

I am just looking for some help correcting the problems with the script. If you could please give me some ways to improve it I would really appreciate it! Oh and I was told that the functions str2num and num2str would come in handy but I do not have any idea where the functions could be used!

Answer 1

[Walter Roberson]

ofn = sprintf('%s%d%s', 'updated_', num, fname);

and fget1 needs to be fgetl (you have the digit 1 instead of lower-case L)

You have

    ln=fget1(ifh);
    if isnumeric(ln)

However, the only time that isnumeric() will be true for the result of fgetl() is if end of file was encountered. isnumeric does not test to see if the input is a string that represents a number: it tests to see if the input is type single(), double(), int8(), int16(), int32(), int64(), uint8(), uint16(), uint32(), or uint64().

... there are other problems as well.

[Kevin Smith]

Okay, I fixed the ones you suggested. What could I use instead of 'isnumeric'? How would you write the while loop?

[Walter Roberson]

If you have broken out a sequence of characters that you will need to convert to numeric form if it represents a number, and you do not know if the sequence does represent a number, then you can use

num = str2double(ln);
if ~isnan(num)

because nan is always returned by str2double() if the characters do not represent a number.

Answer 2

[Stephen23]

First a few notes:

• Processing numeric data that is encoded in character arrays is quite inefficient, and makes the code complex: numeric data should be converted to numeric variables, which then makes all numeric operations on those variables much more efficient.
• Not only is is very inefficient, it also makes it easy to create bugs: your use of isnumeric makes no sense because the variable data type is always going to be character.
• Using a while loop, if and mod to detect the multiples could work, but it is much simpler and more efficient to use indexing.
• Depending on the requirements, you might still need to think about trailing space characters and newlines.
• It is recommended to check the output of fopen, and display the second output if there is any problem opening the file.

Here is a working function which has been tested with your example data:

function replaceMultiples(fname, num)
foutp = sprintf('updated%d %s',num,fname);
[fid,mig] = fopen(fname,'rt');
[fod,mog] = fopen(foutp,'wt');
assert(fid>=3,mig);
assert(fod>=3,mog);
while ~feof(fid)
    str = fgetl(fid);
    vec = sscanf(str,'%f');
    idx = mod(vec,num)==0;
    vec(idx) = vec(idx)/num;
    fprintf(fod,'%d ',vec);
    fprintf(fod,'\n');
end
fclose(fid);
fclose(fod);
end

And tested on your sample data gives this output:

41 571 -11 
14 5 6 
2 3 
28 25 11 12

Both files are attached as well.