MATLAB: How to extract the last rows of specific columns of a text file

text file

Please, I have a text file contains three columns I need to extract the last rows of the third and forth columns only and write them into a text file. for example, from the text file attached the result needs to be written in a text file. it should return:
1.87 36
157 35
1.88 37
1.36 48
1.73 78
1.99 100
Many thanks

Best Answer

Read the data from file, ignoring 1 header line:
 data = cell2mat(textscan(fopen('a.txt'), '%f%f%f', 'headerlines', 1));
Find the last position for each sequence in column 2. The last position is the position where the data changes, i.e., where the difference is > 0. Add 1 to the end get the last position for the last sequence:
idx = find([diff(data(:,2)); 1] > 0);
Now we have the position of the last entry of each sequence in ind. Since we want the last n elements of a sequence, we use the entry x minus n+1, so x -2 in case of n = 3. For the i'th sequence, we want to extract data(ind(i)-2:ind(i), 3). Instead of using a for-loop, we use arrayfun to work on the ind array:
d3 = arrayfun(@(x) (data(x-2:x,3)), idx, 'UniformOutput', false);
The final step is to write the numbers to a file:
 dlmwrite('b.txt', d3)
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