Counting characters in a file

24 vues (au cours des 30 derniers jours)
Hussain Bhavnagarwala
Hussain Bhavnagarwala le 28 Mar 2020
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
  6 commentaires
Image Analyst
Image Analyst le 29 Mar 2020
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
Adam Danz le 29 Mar 2020
Thanks, Image Analyst.

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Réponse acceptée

Adam Danz
Adam Danz le 29 Mar 2020
Modifié(e) : Adam Danz le 30 Mar 2020
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
  11 commentaires
Ameer Hamza
Ameer Hamza le 30 Mar 2020
The condition lower(f) == lower(a) should be carefully used. It is only valid for case-insensitive counting of characters.
Adam Danz
Adam Danz le 30 Mar 2020
Modifié(e) : Adam Danz le 30 Mar 2020
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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Plus de réponses (3)

Rishi Diwan
Rishi Diwan le 23 Mai 2020
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
  3 commentaires
yi yang
yi yang le 4 Sep 2022
a shorter version of your code:
function charnum = char_counter(fname,character)
charnum = count(fileread(fname),character);
end
Walter Roberson
Walter Roberson le 4 Sep 2022
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
Ahsiur Rahman Nirjhar le 24 Mai 2020
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;

Mert Yalcinoz
Mert Yalcinoz le 1 Fév 2022
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
  1 commentaire
Walter Roberson
Walter Roberson le 1 Fév 2022
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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