Assignment question based on excel file I/O

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Ajai Kannan
Ajai Kannan il 17 Feb 2019
Commentato: Rik il 16 Mar 2021
Write a function called get_distance that accepts two character vector inputs representing the names of two cities. The function returns the distance between them as an output argument called distance. For example, the call get_distance('Alexandria, VA' , 'Allentown, PA') should return 195
. If one or both of the specified cities are not in the file, the function returns -1.
download.png
The code I tried is the following:
I get error in the " if text{i,1} == a" and "if text{1,j} == b" lines stating matrix dimensions must agree. Will be really helpful if someone can help me with it.
function distance = get_distance(a,b)
[~,text,raw] = xlsread('Distances.xlsx');
for i = 2 : size(text,1)
if text{i,1} == a
for j = 1 : size(text,2)
if text{2,j} == b
distance = raw{i,j};
else
distance = -1;
end
end
else
distance = -1;
end
end
  4 Commenti
Guillaume
Guillaume il 2 Apr 2019
@sanket,
Loops are not needed at all for this. strcmp is perfectly capable of the searching a whole cell array at once.
Walter Roberson
Walter Roberson il 2 Apr 2019
This code is wrong for the case where the match is the last row or column. You break out of the loop but the value of the index happens to exactly equal to the size so you think there was no match.

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Risposte (7)

Geoff Hayes
Geoff Hayes il 17 Feb 2019
Ajai - if you try to compare strings using the == operator, then you will see this error if the two strings being compared are of different lengths. Instead, you should be using strcmp or strcmpi to check for equality between two strings. Your code would then change from
text{i,1} == a
to
strcmp(text{i,1}, a)
Also, rather than using a loop, you could use find to see if the first column of text contains the cities that you are looking for (see the examples in the provided link for details).
  4 Commenti
Priyamvada Shankar
Priyamvada Shankar il 23 Mar 2019
Ajai Kannan if you got the correct code.. please post here
Walter Roberson
Walter Roberson il 23 Mar 2019
This is obviously an assignment. We seldom post the code to answer assignments. However, if you post your attempt and indicate the error messages you are encountering, then we will assist you in debugging what you have.

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ABINAND PANDIYAN
ABINAND PANDIYAN il 24 Apr 2020
Modificato: ABINAND PANDIYAN il 25 Apr 2020
% This problem is right I think.
function distance = get_distance(A,B)
[~,~,dist] = xlsread('Distances.xlsx');
for i=2:(size(dist,1)+1)
if i>size(dist,1)
distance=-1;
return
end
if strcmp(dist{i,1}, A)
break
end
end
for j=2:(size(dist,2)+1)
if j> size(dist,2)
distance=-1;
return
end
if strcmp(dist{1,j}, B)
distance=dist{i,j};
break
end
end
end
  2 Commenti
Walter Roberson
Walter Roberson il 24 Apr 2020
Suppose that A happens to exactly match the city name in the last row. Then i = size(dist,1) and success would be desired. The for loop would execute and on the last iteration, strcmp(dist{i,1},A) would succeed, so you would break; with i = size(dist,1). Then you do if i>=size(dist,1) and find that i == size(dist,1) so the if succeeds, and you declare the distance to be -1 and return, even though you had a match.
In the case where there was no match at all, the for i loop would complete, and afterwards i would be size(dist,1), same as if there had been a match on the last item. You test i>=size(dist,1) and that is true so you return -1, same as the case where you had a city match on the last row.
In MATLAB, after a for loop, if the body of the for did not change the loop variable, then the loop control variable is left at the last value it had, not one more than the last value it had. You will need to fix that termination condition.
ABINAND PANDIYAN
ABINAND PANDIYAN il 25 Apr 2020
Modificato: ABINAND PANDIYAN il 25 Apr 2020
@Walter Roberson
Yeah I checked that, But now after hours of brainstroming I think I got the answer right with the edited content. You can check it now.

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Olel Arem
Olel Arem il 1 Mag 2020
Modificato: Olel Arem il 1 Mag 2020
function distance=get_distance(city_1,city_2)
n=0;m=0;
[value,name]=xlsread('Distances.xlsx');
for ii=1:size(name,2)
if (strcmp(city_1,name(ii,1)))
n=ii;
end
end
for jj=1:size(name,1)
if (strcmp(city_2,name(1,jj)))
m=jj;
end
end
if(n==0 && m==0 && n==1&&m==1)
distance =-1;
elseif (n>0&&m>0)
distance=value(n-1,m-1);
else
distance=-1;
end

Fazlul Haque
Fazlul Haque il 15 Mag 2020
done without using loops
  8 Commenti
Farhaan Zaidi Bhat
Farhaan Zaidi Bhat il 13 Dic 2020
Modificato: Farhaan Zaidi Bhat il 13 Dic 2020
Can you please explain the a and b steps? The data part?
Rik
Rik il 13 Dic 2020
Did you read the documentation for the strcmpi function?

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Muhammad Qaisar Ali
Muhammad Qaisar Ali il 27 Giu 2020
function distance = get_distance(city_1,city_2)
persistent distt city_names;
if isempty(distt) && isempty(city_names) % Ceck wheater first time load or not.
[distt,city_names,~]=xlsread('Distances.xlsx'); % Reading ditances and names of cities
end
rowIndex = find(ismember(city_names(:,1),city_1)); % Searching city_1 in col_1 of excell seet.finding row index.
colIndex = find(ismember(city_names(1,:),city_2)); % Searching city_2 in row_1 of excell seet.finding col index.
if isempty(rowIndex) || isempty(colIndex) % If cities nit found return -1.
distance=-1;
else % Find and retun distance.
distance=distt(rowIndex-1,colIndex-1);
end
end
  2 Commenti
Walter Roberson
Walter Roberson il 27 Giu 2020
Caching the data is often a good performance improvement, but remember to document the method that would need to be used to signal that the Distances file had changed.
Muhammad Qaisar Ali
Muhammad Qaisar Ali il 28 Giu 2020
Thanks for your vaulable feedbak..indeed it helps me alot..

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Priyamvada Shankar
Priyamvada Shankar il 22 Mar 2019
Can you please write the code...it will be a great help... please I have tried too many times but still getting some problems
  7 Commenti
Walter Roberson
Walter Roberson il 29 Mar 2019
You want to find some way to break out of the loop early.
sadek kouz
sadek kouz il 18 Mar 2020
Modificato: sadek kouz il 18 Mar 2020
use break to break out of the looo

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XINYI CAI
XINYI CAI il 16 Mar 2021
why my answer does not work for non-exsitent city?
  3 Commenti
XINYI CAI
XINYI CAI il 16 Mar 2021
@Rikoh i see, variables row and column are arrays with a number of 0 instead of empty arrays, I should change column=value1==1 to coulmn=find(value1==1) and the same for variable row, then it makes sense. tq
Rik
Rik il 16 Mar 2021
No, you should use ~any(row) instead.

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