Counting characters in a file

Hello,

I am doing an online course on matlab in coursera and I have come a cross a problem that seems hard for me to solve.

I need to write a function that takes the name of the text file and a paticular charater as input and then the function must count how many times the character is present in the file and return that number.

function charnum = char_counter(b,a)
    fid = fopen(b,'r');
    if fid < 0 || ~ischar(a) || length(a) == 0
        charnum = -1;
        return
    end
    t=0;
    d=1;
    while (d>0)
        d = fgetl(fid);
        x = strfind(d,a);
        t = t + length(x);
    end
    charnum = t;    
    fclose(fid);
end

I have passed 3 out of 4 checks, following is the error that I am getting

Variable charnum has an incorrect value. When testing with ' ' your solution returned 1 which is incorrect. (75444).

I tried countin the number of " ' ' " as well and it seemed correct to,

I would like to the mistake that I am making.

Thanks

Hussain

[Ameer Hamza]

Can you give the function call when the function fails. What are the values of a and b.

[Hussain Bhavnagarwala]

The moderator of the forum said that It does not count spaces " ", but I tried that and it does, so I am not sure.

I am unable to see the inputs to the function. I can only see the errors

[Ameer Hamza]

I am not sure about the issue. Maybe you can try this loop-free version.

char_counter('text.txt', ' ')

function charnum = char_counter(b,a)
    fid = fopen(b,'r');
    if fid < 0 || ~ischar(a) || isempty(a)
        charnum = -1;
        return
    end
    data = char(fread(fid)');
    charnum = numel(strfind(data, a));
    fclose(fid);
end

[Adam Danz]

I don't want to give the answer away because this is an assignment but this can be done with 1 line of code.

Hints:

1. fileread() returns a char array
2. sum(chararray == 'c')
3. For case insensitivity, upper() or lower()

[Image Analyst]

Adam, I'd put that down in the answer section so you can get credit for it. I was about to say the same thing.

[Adam Danz]

Thanks, Image Analyst.

Answer 1

[Adam Danz]

Here's a demo to count the instances of a character in a text file.

This demo searches for a space character ' ' and then replaces the space characters with squares so you can visually confirm the results.

This is the simple text file I'm reading in (also attached).

Read in the file and count the empty spaces ' '

idx shows the location of spaces.

c = fileread('myTextFile.txt'); 
idx = c == ' '; 
sum(idx)
% ans =
%     67

To search for a case insensitive character, use upper() or lower().

idx = lower(c) == 'a'; 

Replace the spaces with squares

cCopy = c; 
cCopy(idx) = char(746);  % square character
disp(cCopy)

Spaces have been replaced with squares. Number of squares = 67

[Hussain Bhavnagarwala]

Hi adam ,

Thanks for taking the time to write a solution

function charnum = char_counter1(b,a)
    fid = fopen(b,'r');
    if fid < 0 || ~ischar(a) || isempty(a)
        charnum = -1;
        return
    end
    f = lower(fileread(b));
    charnum = sum(f=='a');
    fclose(fid);
end

I am still getting a similar error :

Variable charnum has an incorrect value.

When testing with ' ' your solution returned 25788 which is incorrect. (75444)

I tried this function from @ameer hamza

data = char(fread(fid)');
charnum = numel(strfind(data, a));
fclose(fid);

This one seems to work, but I don not understand why ?( I would like to know as it will help me in the future)

Thanks

Hussain

[Ameer Hamza]

Hussain, I think you should try after removing the lower function from this code

f = fileread(b);
charnum = sum(f==a);

[Hussain Bhavnagarwala]

I am getting the following error

Variable charnum has an incorrect value.
When testing with ' ' your solution returned 25433 which is incorrect. (75444)

[Ameer Hamza]

Can you paste your code here. There was another issue in your pasted code. Change

charnum = sum(f=='a');

to

charnum = sum(f==a);

[Hussain Bhavnagarwala]

Yes that was it !....

I feel so stupid now ....

[Adam Danz]

Your previous results returned the number of "a" characters.

I've updated my answer now that you've solved it using the method I was hinting at.

You'll notice that you don't need any of the fid parts of your code. In fact, your function can be reduced to one line.

[Hussain Bhavnagarwala]

I think the fid part was needed to check if the file had any content, the prompt had told us that we need to return -1 if the file is empty

[Adam Danz]

You could do the same thing using

function charnum = char_counter1(b,a)
f = fileread(b); 
if isempty(f)
    charnum = -1;
else
    charnum = sum(lower(f) == lower(a));
end

That's the entire function.

[Hussain Bhavnagarwala]

I have miles to go in matlab I guess !!

[Ameer Hamza]

The condition lower(f) == lower(a) should be carefully used. It is only valid for case-insensitive counting of characters.

[Adam Danz]

OP's code shared here shows

f = lower(fileread(b));
charnum = sum(f=='a');

which indicates a case insensitive search. There's no use in doing that unless the search key is also case insensitive. But it's good to explicitly point that out for the OP.

With an empty space search, case doesn't matter since upper(' ')==lower(' ').

Answer 2

[Rishi Diwan]

function charnum = char_counter(fname,character) 
fid = fopen(fname,'rt');
if fid <= 0 || ~ischar(character) || ~ischar(fname) || length(fname)==0 || length(character)==0 || isempty(fname) || isempty(character)
    charnum=-1;
    return;
end
    c=0;
ol=fgets(fid);
while ischar(ol) 
    c=c+count(ol,character);
    ol=fgets(fid);
end
charnum=c;
fclose(fid);
end

[Walter Roberson]

if the file open succeeded but the other parameter is not a valid character then you are leaving the file open.

[yi yang]

a shorter version of your code:

function charnum = char_counter(fname,character)
charnum = count(fileread(fname),character);
end

[Walter Roberson]

@yi yang

This turns out to be a homework assignment. The checks for file existing and for the input being a valid character are required as part of the assignment.

Answer 3

[Ahsiur Rahman Nirjhar]

function x=char_counter(a,b)
fid=fopen(a,'rt');
if fid <0 || ~ischar(b)
    s=-1;
else
    s=0;
    oneline=fgets(fid);
    while ischar(oneline)
       
        s=s+sum(double(oneline)==double(b));
        oneline=fgets(fid);
    end
    fclose(fid);
   
end
x=s;

Answer 4

[Mert Yalcinoz]

By looking other's people answers i have combined my code and got the result.

function charnum=char_counter(fname,character) %creating function
fid=fopen(fname,'rt');
if fid<0 || ~ischar(character) || length(character)==0 %conditions
    charnum=-1;
    return
end
a=0; %setting a total value for found desired string 
b=fgets(fid); %for reading the first line, returns single line in a string
while ischar(b) %loop for each line 
    a=a+count(b,character); %summing when a character is found
    b=fgets(fid); %if there is no new line, b becomes -1 and loop ends.
end
charnum=a; %setting output variable
fclose(fid);
end

[Walter Roberson]

Suppose that a valid file name is passed in, but suppose that character is not a valid character or is empty. Then you set charnum=-1 and return... without having closed the file.