Python for loop savetxt 每次迭代都在一个文件中

Question

I am trying to load two txt files, each file only has one column. Then I do things for each of the file and output two columns/rows for each analysis. I want to save all iterations in the for loop. In this case the output file would have four columns/rows. Here is what I got that didn't work

filelist=["1.txt","2.txt"]
results=[]

for file in filelist:
    a= np.loadtxt(file) 
    do things
    sol = rungekutta4(....)
    Theta = (t4, sol[:, 0])
    savetxt('results.csv', results.append(Theta), delimiter=',')

Answer 1

It is possible to append to a file for each iteration of a loop without numpy .

filelist=["1.txt","2.txt"]
results=[]

for file in filelist:
    a= np.loadtxt(file) 
    
    ...
    
    #savetxt('results.csv', results.append(Theta), delimiter=',')
    with open('outFilename.csv', 'a') as file: # the 'a' means to append to the end of the file:
        file.write(','.join(results)) # the '[separator]'.join(list) converts a list into a string, with each item separated by [separator]

Just to be clear, the for loop will output the results variable for each iteration.

Here is an example of the output:

a
a,b
a,b,c
a,b,c,d

Note that since the file is being opened over and over again many times, you may find the loop slow for a large number of iterations.

To fix this, you can also open the file at the very beginning of the file, just once.