Counting characters in a file

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Hussain Bhavnagarwala 2020-3-28

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https://ww2.mathworks.cn/matlabcentral/answers/513523-counting-characters-in-a-file

评论： Walter Roberson 2022-9-4

采纳的回答： Adam Danz

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

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Image Analyst 2020-3-29

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 2020-3-29

Thanks, Image Analyst.

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采纳的回答

Adam Danz 2020-3-29

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https://ww2.mathworks.cn/matlabcentral/answers/513523-counting-characters-in-a-file#answer_422699

编辑：Adam Danz 2020-3-30

myTextFile.txt

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

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Ameer Hamza 2020-3-30

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

Adam Danz 2020-3-30

编辑：Adam Danz 2020-3-30

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(' ').

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更多回答（3 个）

Rishi Diwan 2020-5-23

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/513523-counting-characters-in-a-file#answer_436708

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

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yi yang 2022-9-4

a shorter version of your code:

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

Walter Roberson 2022-9-4

@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.

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Ahsiur Rahman Nirjhar 2020-5-24

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https://ww2.mathworks.cn/matlabcentral/answers/513523-counting-characters-in-a-file#answer_437343

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;

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Mert Yalcinoz 2022-2-1

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/513523-counting-characters-in-a-file#answer_886100

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

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Walter Roberson 2022-2-1

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.

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