Why Using '%f' as formatspec for a text file containing floating numbers gives no output

Question

Zhou Ci 2021-9-1

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1444469-why-using-f-as-formatspec-for-a-text-file-containing-floating-numbers-gives-no-output

回答： KSSV 2021-9-1

Hello everyone,

I want to read data fom a text file. Text file contains different rows and column. I used below lines of code to read the data but it returns an empty A:

fileID = fopen('Data.txt', 'r');
  formatSpec = '%f';
 A = fscanf(fileID, formatSpec);

Secondly, I just want values of t where lat and lon equals:

lat = 32.4876 32.4909

lon = 117.5421 117.5739

Thank you.

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Answer 1

Walter Roberson 2021-9-1

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https://ww2.mathworks.cn/matlabcentral/answers/1444469-why-using-f-as-formatspec-for-a-text-file-containing-floating-numbers-gives-no-output#answer_778464

在 MATLAB Online 中打开

target_lats = [32.4876 32.4909];
target_lons = [117.5421 117.5739];
filename = 'https://www.mathworks.com/matlabcentral/answers/uploaded_files/726444/Data.txt';
A = readtable(filename, 'readvariablenames', true, 'VariableNamingRule', 'preserve')
A = 5×17 table
    col    row     1.8      0.5      1.6      1.1       t       tt      8.0t     9.7t      t0       ssf     ph    3.7r      r      lat       lon  
    ___    ___    _____    _____    _____    _____    _____    _____    _____    _____    _____    _____    __    _____    ___    ______    ______

    241    169    0.476    0.143    0.236    0.121    313.3    251.7    293.4    271.7      293    302.4    0     0.184    0.5    32.485    117.62
    236    170    0.506    0.163    2.399     0.08    300.1    246.7    279.9    262.4    278.7    285.5    0     0.102    0.5    32.488    117.54
    237    170     0.52    0.154    2.399    0.084    302.7    248.5    283.6    265.1    282.6    290.3    0     0.112    0.6    32.489    117.56
    238    170    0.505    0.149    2.399    0.077    303.2    248.7    284.2    265.4    283.4    291.8    0     0.114    0.8    32.491    117.57
    239    170    0.265    0.151    2.399    0.048      302    248.9    284.3    265.6    283.3    291.4    0     0.103    0.1    32.492    117.59
mask = ismembertol(A.lat, target_lats) & ismembertol(A.lon, target_lons);
selected_t = A.t(mask)
selected_t = 2×1
  300.1000
  303.2000

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Walter Roberson 2021-9-1

But to answer your question:

You did not skip any input lines, so your %f was trying to read starting from the very first thing in the file. But the very first thing in the file is the word 'col' which is something that cannot be read with a %f format, so MATLAB stopped reading. fscanf() only continues to read items as long as the format matches, but the word 'col' does not match %f format.

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Answer 2

KSSV 2021-9-1

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1444469-why-using-f-as-formatspec-for-a-text-file-containing-floating-numbers-gives-no-output#answer_778469

在 MATLAB Online 中打开

data = importdata('data.txt') ; 
data = data.data ;
t = data(:,7) ; 
x = data(:,17) ; 
y = data(:,16) ; 
lat = [32.4876 32.4909] ; 
lon = [117.5421 117.5739] ;
t_lon = interp1(x,t,lon) ; 
t_lat = interp1(y,t,lat) ;