file handling with coordinates

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Edgar Gonzalez 2018-10-12

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评论： jonas 2018-10-15

cities.txt

I have to write a code that organizes a text file filled with coordinates and organize them by latitude or longitude for each state(EX: CA would be North-South and Tennessee would be East-West) and then print out the cities in order by distance for whichever state the user inputted. I have attached the text file. I am not expecting somebody else to do the work for me. I just don't know where to start. Specifically I don't know how I would go about beginning to organize the cities per state.

Any and all help would be greatly appreiciated. Thank you!

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jonas 2018-10-12

I dont really understand the problem you are facing. Can you elaborate?

Edgar Gonzalez 2018-10-12

编辑：Edgar Gonzalez 2018-10-12

在 MATLAB Online 中打开

Screen Shot 2018-10-12 at 2.18.56 PM.png

I attached a screeshot of the assignment maybe that can help. This is the code I have as of now. A lot of it is probably wrong. Right now I was just attempting to get the correct syntax down

    % Project 1
fid = fopen('cities.txt', 'r'); % opens the file with read permission
state = input('Which state are you visiting ','s');
found = false; 
while ~found && ~feof(fid) % tests for end of file
  l=fgets(fid);
if ~contains(l,state), continue, end  % keep going until found
lat_deg = str2double(l(1:2)); % defines variables for coordinates
lat_min = str2double(l(4:5));
long_deg = str2double(l(8:9));
long_min = str2double(l(11:12));
switch state
    case 'Alabama'
        fprintf('hi')
end
end

fclose(fid)

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Answer 1

jonas 2018-10-12

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编辑：jonas 2018-10-12

I would approach this roughly as follows:

Read all coordinates and group them by state
Use a grouping function ( findrows/ splitapply, varfun, grpstats) to calculate the max/min long/lat in each state (4 values per state
If you have the mapping toolbox, calculate the east-west and north-south arclength to find the longest distance.
Use a grouping function again to output a sorted list of cities per state that is returned to the user upon request.

Try yourself, and ask if you have trouble with one of the steps.

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Edgar Gonzalez 2018-10-15

编辑：Walter Roberson 2018-10-15

This is what I decide to try. I want to print all lines of the text file that contain both the state and the assigned lat or long value given in the switch case. I know lgets works for when you want to find 1 matching value. How can I write it to work for both? (ex: find all lines in the file that contain California and a longitude of 120)

% Project 1
fid = fopen('cities.txt', 'r'); % opens the file with read permission
state = input('Which state are you visiting ','s');
found = false; 
while ~found && ~feof(fid) % tests for end of file
    switch state
      case 'Alabama'
          long = 87;
      case 'Alaska' 
          long = 152;
      case 'Arizona'
          long = 111;
      case 'California'
          long = 120;
      case 'Colorado'
          lat = 39;
      case 'Connecticut'
          lat = 42;
      case 'Delaware'
          long = 76;
      case 'Florida'
          long = 82;
      case 'Georgia'
          long = 84;
      case 'Hawaii'
          lat = 21;
      case 'Idaho'
          long = 114;
      case 'Illinois'
          long = 89;
      case 'Indiana'
          long = 86;
      case 'Iowa'
          lat = 42;
      case 'Kansas'
          lat = 39;
      case 'Kentucky'
          lat = 38;
      case 'Louisiana'
          long = 92;
      case 'Maine'
          long = 69;
      case 'Maryland'
          long = 77;
      case 'Massachusetts'
          lat = 42;
      case 'Michigan'
          long = 85;
      case 'Missouri'
          long = 92;
      case 'Montana'
          lat = 47;
      case 'Nebraska'
          lat = 41;
      case 'Nevada'
          long = 117;
      case 'New Hamphsire'
          long = 72;
      case 'New Jersey'
          long = 75;
      case 'New Mexico'
          long = 106;
      case 'New York'
          lat = 42;
      case 'North Carolina'
          lat = 36;
      case 'North Dakota'
          lat = 48;
      case 'Ohio'
          lat = 40;
      case 'Oklahoma'
          lat = 36;
      case 'Oregon'
          lat = 45;
      case 'Pennsylvania'
          lat = 41;
      case 'Rhode Island'
          long = 72;
      case 'South Carolina'
          lat = 34;
      case 'South Dakota'
          lat = 44;
      case 'Tennessee'
          lat = 36;
      case 'Texas'
          lat = 31;
      case 'Utah'
          long = 112;
      case 'Vermont'
          long = 73;
      case 'Washington'
          lat = 47;
      case 'West Virginia'
          long = 81;
      case 'Wisconsin'
          long = 90;
      case 'Wyoming'
          lat = 43;
  end

    l=fgets(fid);

    if ~contains(l,state), continue, end % keep going until found
    lat = str2double(l(1:2)); % defines variables for coordinates
    lat_min = str2double(l(4:5));
    long = str2double(l(8:9)); 
    long_min = str2double(l(11:12));
  end

fclose(fid);

Walter Roberson 2018-10-15

Have you considered creating a vector of target lat or long values, and a cell array of character vectors with the names of the states? And use ismember() to match the input state to the name list, getting out an index (second output of ismember) that you use to index the lat or long array?

I do not know what those lat or long values are doing for you? And I am concerned because you have not defined both of them for each state, which always leads to the risk that you could accidentally use a value appropriate for the previous state.

jonas 2018-10-15

That does not look optimal. Where did you get those coordinates from? Is it the "length" of the state in units of degrees? Do you know that you cannot compare latitude and longitude in absolute terms? You should compare arclength if you want to calculate the "length" of the state.

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