Read the column 2 and 11 from 45 csv files in 45 subfolder hence plot them.

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muhammad choudhry
评论： KSSV 2022-7-6
Hi,
I am using the code below to plot the diatance over U from 45 csv files but as soon as I am running it matlab is crashing.
What I want from the code. is to read all 45 csv files, extract 45 (column 2 and column 11 from the files and plot all in one graph)
Code:
close all; clear all; clc;
projectdir = 'F:\3-PIV_Experimental_Data\Outlet_110\Data_LaserSheet_D\Data_PIV\6-VectorSatistics\PlotOverLine';
files = dir( fullfile(projectdir, '*', '*.csv') );
filenames = fullfile({files.folder}, {files.name});
num_files = length(filenames);
Distance = zeros(num_files,1);
U = zeros(num_files,1);
for i = 1:numel(files);
filename = filenames{i};
data = readtable(filename);
Distance(i) = table2array (data(:,2));
U(i) = table2array (data(:,11));
end
Plot(Distance,U)
Error:
Unable to perform assignment because the left and right sides have a different number of elements.
Error in BONO1_LSD (line 22)
Distance(i) = table2array (data(:,2));
  1 个评论
Aman Banthia
Aman Banthia 2022-7-6
Hello,
Can you try removing semi colon at the end of for statement
for i = 1:numel(files)
filename = filenames{i};
data = readtable(filename);
Distance(i) = table2array (data(:,2));
U(i) = table2array (data(:,11));
end
Try to use it like this.

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采纳的回答

KSSV
KSSV 2022-7-6
编辑：KSSV 2022-7-6
Save the data into cells. If each file has different dimension.
close all; clear all; clc;
projectdir = 'F:\3-PIV_Experimental_Data\Outlet_110\Data_LaserSheet_D\Data_PIV\6-VectorSatistics\PlotOverLine';
files = dir( fullfile(projectdir, '*', '*.csv') );
filenames = fullfile({files.folder}, {files.name});
num_files = length(filenames);
Distance = cell(num_files,1);
U = cell(num_files,1);
figure
hold on
for i = 1:numel(files);
filename = filenames{i};
data = readtable(filename);
Distance{i} = table2array (data(:,2));
U{i} = table2array (data(:,11));
plot(Distance{i},U{i})
end
If the number of rows in each file is same and you know the number of rows.
close all; clear all; clc;
projectdir = 'F:\3-PIV_Experimental_Data\Outlet_110\Data_LaserSheet_D\Data_PIV\6-VectorSatistics\PlotOverLine';
files = dir( fullfile(projectdir, '*', '*.csv') );
filenames = fullfile({files.folder}, {files.name});
num_files = length(filenames);
N = 100 ; % where N is number of rows in each file
Distance = zeros(N,num_files);
U = zeros(N,num_files);
for i = 1:numel(files);
filename = filenames{i};
data = readtable(filename);
Distance(:,i) = table2array (data(:,2));
U(:,i) = table2array (data(:,11));
end
plot(Distance,U)

更多回答（2 个）

Karim
Karim 2022-7-6
Distance(i) = table2array(data(:,2));
Here you are trying to store an entire array into a single placehoder. Unless data(:,2) is a scalar, this wont work.
If the size is the same for all files you can initialize Distance as a matrix:
Distance = zeros(num_files, num_rows_data);
in the loop you need to change the indexing to
Distance(i,:) = table2array(data(:,2));
If the files have different sizes, then you can save the data into a cell array. In this case allocate as
Distance = cell(num_files, 1);
and save data as
Distance{i} = table2array(data(:,2));
Walter Roberson
Walter Roberson 2022-7-6
Distance(i) = table2array (data(:,2));
table2array() of a table with a single numeric variable, is going to produce one row of output for each row in data . You are expecting to store that entire row of output in the single numeric location Distance(i)
I suggest
Distancec = cell(num_files,1);
Uc = cell(num_files,1);
for i = 1:numel(files);
filename = filenames{i};
data = readtable(filename);
Distancec{i} = table2array (data(:,2));
Uc{i} = table2array (data(:,11));
end
Distance = cell2mat(Distancec);
U = cell2mat(Uc);
plot(Distance, U)
... Except that I suspect you will find that confusing, as there will be no breaks between the files.
Do you want one line per file? If so then try
hold on
cellfun(@(d,u) plot(d,u), Distancec, Uc);
legend(filenames);
hold off
xlim auto; ylim auto

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