Merge array lists into one array list

Question

I spent more time on this issue than I am willing to admit. I have a function called:

def array_funct(filename):
...
 data = np.array((array))
 return data

which reads in .txt files from a folder and returns a numpy array.

The first row is a list of x coordinates and second row are the cooresponding y coordinates. Hence I use:

array_funct(filename)[:,0]
array_funct(filename)[:,1]

to access the x and y coordinates.

Now all I want to do is to create a for loop which would read in more than 1 file and store them in following way

for i in range(0,number_of_files):

    array_funct(file[i])[:,0]
    array_funct(file[i])[:,1]

Let's look at the x-lists which I get:

print(array_funct(file[0])[:,0])  
[1,2,3,4]
print(array_funct(file[1])[:,0]) 
[2,4,6,8]

All I want is to take these two numpy like lists and create:

x_tot = [[1,2,3,4], [2,4,6,8]]

such that I can access the single lists element wise like:

x_tot[0] = [1,2,3,4]

Is that so hard? Should I stop using numpy array ? I would like to stay in numpy if possbile.

Also keep in mind that I made this example for just 2 files but it could be more. I just want to create a x_tot and y_tot for a variable amount of files I would read in. Such that:

x_tot = [[1,2,3],[2,3,4],[..],..]
x_tot = [[2,4,6],[4,6,8],[..],..]

Massifox · Accepted Answer · 2019-09-26 13:03:43Z

2

Given the following array_funct function and filenames list:

def array_funct(filename):
    # Fake random data, replace with data read from file
    data_read = [[1,2,3,4], [5,6,7,8]] # [random.sample(range(1, 10), 7), random.sample(range(1, 10), 7)]  
    data = np.array(data_read) 
    return data

filenames = ['file1.txt', 'file2.txt']

Try this code:

lx = [list(array_funct(file)[0]) for file in filenames]
ly = [list(array_funct(file)[1]) for file in filenames]

Or more efficiently by reading and scrolling the file once:

all_data = [(list(arr[0]),list(arr[1])) for arr in [array_funct(f) for f in filenames]]
lx, ly = list(map(list, zip(*all_data)))

In both cases, the output is as follows:

# lx = [[1, 2, 3, 4], [1, 2, 3, 4]]
# ly = [[5, 6, 7, 8], [5, 6, 7, 8]]

edited Sep 26, 2019 at 13:03

answered Sep 26, 2019 at 12:51

Massifox

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Comments

FabioL · Accepted Answer · 2019-09-26 09:05:00Z

1

Something like:

x_tot = np.array([array_funct(file[i])[:,0] for i in range(0,number_of_files)])

should work.

answered Sep 26, 2019 at 9:05

FabioL

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4 Comments

Benjamin Jabl Over a year ago

It works but it also includes the word 'array'. Is that a problem? [array([ 16863.2, 23735. , 107915.1, 52643.9, 68688.5, 74618.5, 94618.5]) array([ 16864.3, 23737.3, 107917.4, 52645.7, 68690.8, 74620.6])]

FabioL Over a year ago

From array_funct(file[i])[:,0] you obtain a numpy array (that is the reason of 'array' word), I made a list comprehension to join the numpy array for every file and, finally, because you said that you would like to stay in numpy I converted the list in numpy array with np.array().

Benjamin Jabl Over a year ago

You are right and on paper it should work. But I am getting a 'ValueError: setting an array element with a sequence.' BUT it works if I were to use a regular np list like x_tot = [[1,2,3],[2,3,4]] for example. Something is not quite working

Benjamin Jabl Over a year ago

Funny. A file like [list([1, 2, 3, 4, 5, 9, 8, 7]) list([5, 4, 10, 11, 3]) list([3, 6, 7, 12, 7, 9])] which is also a np object can be read in, no problem. But [array([ 16863.2, 23735. , 107915.1, 52643.9, 68688.5, 74618.5, 94618.5]) array([ 16864.3, 23737.3, 107917.4, 52645.7, 68690.8, 74620.6])] CANNOT be read in. Why...

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