Appending Int to an Array Matlab - arrays

Question

I am using an API to get real data times of trains and am trying to get the closest train time to a user entered time and then display that train time, and the next 4 granted the trains are running. I am reading in the information and the code goes through what its supposed to do but when I look at the array its a bunch of [] brackets in 7 cells instead of the calculated numbers. Any suggestions? Code is below with the API
TEST VALUES:
requestStationSelected = 'University%20City' and requestEndStation = 'Roslyn'
%this is the API link for the live data from Septa this will get 30
%results and see which time is closer to the user entered time
requestInfoSeptaLive = ['http://www3.septa.org/hackathon/NextToArrive/' requestStationSelected '/' requestEndStation '/30'];
%Again tries to get the information and if there is a failure it will give
%a probable cause and terminate the program
try
getInfoSeptaLive = urlread(requestInfoSeptaLive);
catch
if getInfoSeptaLive ~= '[]'
disp...
('Either the arrival/depart stations dont quite match up or theres a server error. Try again.');
return;
else
disp('Unable to fetch the information from Septa, please try again')
return;
end
end
%parses the information returned from the Live API
dataReturnedFromLiveAPI = parse_json(getInfoSeptaLive);
dataReturnedFromLiveAPI = dataReturnedFromLiveAPI{1};
%gets the size of the API in case there are no trains running
sizeOfDataNoTrains = size(dataReturnedFromLiveAPI, 1);
sizeOfData = size(dataReturnedFromLiveAPI, 2);
counter = 0;
for i = 1:sizeOfData
scanForClosestTime = dataReturnedFromLiveAPI{1,i}.orig_departure_time;
trainTimeGivenH = sscanf(scanForClosestTime, '%i');
findColonTrain = strfind(scanForClosestTime, ':');
trainTimeGivenMStr = scanForClosestTime(findColonTrain+1:4);
trainTimeGivenM = int32(str2num(trainTimeGivenMStr));
trainDepartTimeM = (trainTimeGivenH(1,1) * 60) + (trainTimeGivenM);
differenceBetweenTimes = trainDepartTimeM - userEnteredMins;
if trainDepartTimeM < userEnteredMins
differenceBetweenTimes = userEnteredMins - trainDepartTimeM;
end
stopAtEndOfData = sizeOfData;
goodTimeFrame = 60;
closestTime = cell(1, stopAtEndOfData);
storeTheDifference = cell(1, stopAtEndOfData);
if(differenceBetweenTimes < 60)
if (counter < 5)
closestTime{i} = scanForClosestTime;
storeTheDifference{i} = differenceBetweenTimes;
counter = counter + 1;
end
end
end

Answer 1

You assign your cell arrays inside the for loop:
for i = 1:sizeOfData
...
closestTime = cell(1, stopAtEndOfData);
storeTheDifference = cell(1, stopAtEndOfData);
...
end
This means that you turn both of them into an array of {[],[],[],[],[]...} on every iteration of the loop - so unless the last iteration has a valid "closest Time" in it, your cell array will be all empty arrays - and if it does, all but the last element will still be [].
To fix this, move the two lines to before the start of the for loop.
The second problem seems to be the indexing of the arrays where you store the results. If you only want five results, I am assuming you want to store them in elements 1 - 5 of your array, and not in "just any" locations. I would change the code to
if (counter < 5)
counter = counter + 1;
closestTime{counter} = scanForClosestTime;
storeTheDifference{counter} = differenceBetweenTimes;
end
But maybe I misinterpreted how you want to handle that?
Unrelated to your question, you might want to take a look at the line
trainTimeGivenMStr = scanForClosestTime(findColonTrain+1:4);
It is quite possible that this is not what you intended to do - looking at an example of the response, I found the string "orig_departure_time":"11:57PM". I expect that findColonTrain == 3, so that the above line becomes
trainTimeGivenMStr = scanForClosestTime(4:4);
just a single character. Perhaps you meant
trainTimeGivenMStr = scanForClosestTime(findColonTrain+(1:4));
which would turn into
trainTimeGivenMStr = scanForClosestTime(4:7);
so that
trainTimeGivenMStr = '57PM';
I hope these three things help you get it all working!
EDIT: had a chance to run your code this morning - discovered a number of other problems. I include below an annotated "working" code: the biggest problem was most likely that you were not handling AM/PM in your code. Note that I used a different json parser - this changed a couple of lines very slightly. I'm sure you can put it back together to work the way you want. This returned valid data in all cells.
dataReturnedFromLiveAPI = loadjson(getInfoSeptaLive);
% next line not needed - loadjson returns struct array, not cell array
%dataReturnedFromLiveAPI = dataReturnedFromLiveAPI{1};
%gets the size of the API in case there are no trains running
sizeOfDataNoTrains = size(dataReturnedFromLiveAPI, 1);
sizeOfData = size(dataReturnedFromLiveAPI, 2);
counter = 0;
stopAtEndOfData = sizeOfData;
closestTime = cell(1, stopAtEndOfData);
storeTheDifference = cell(1, stopAtEndOfData);
userEnteredMins = 12*60+30; % looking for a train around 12:30 pm
for ii = 1:sizeOfData
scanForClosestTime = dataReturnedFromLiveAPI(ii).orig_departure_time;
trainTimeGivenH = sscanf(scanForClosestTime, '%i');
% since we'll be considering AM/PM, have to set 12 = 0:
if (trainTimeGivenH == 12), trainTimeGivenH = 0; end
findColonTrain = strfind(scanForClosestTime, ':');
% change next line to get minutes plus AM/PM:
trainTimeGivenMStr = scanForClosestTime(findColonTrain+(1:4));
% look at just minutes:
trainTimeGivenM = int32(str2num(trainTimeGivenMStr(1:2)));
% adjust for AM/PM:
if(trainTimeGivenMStr(3:4)=='PM'), trainTimeGivenH = trainTimeGivenH+12; end;
% compute time in minutes:
trainDepartTimeM = (trainTimeGivenH * 60) + (trainTimeGivenM);
differenceBetweenTimes = trainDepartTimeM - userEnteredMins;
if trainDepartTimeM < userEnteredMins
differenceBetweenTimes = userEnteredMins - trainDepartTimeM;
end
% added a couple of lines to see what is happening:
fprintf(1, 'train %d: depart %s - in minutes this is %d vs user entered %d\n', ...
ii, scanForClosestTime, trainDepartTimeM, userEnteredMins);
goodTimeFrame = 60;
if(differenceBetweenTimes < 600)
if (counter < 10)
counter = counter + 1;
closestTime{counter} = scanForClosestTime;
storeTheDifference{counter} = differenceBetweenTimes;
end
end
end