How to merge the list in python

Question

I already read this, this, and this, but no solution.

I have a list of 50 lists like this:

dataTest=[List1,List2,List3,...,List50]

Each of those lists is a list of images along with labels. I mean the first dimension of List1 is consists of some images, and the second dimension of the List1 is their corresponding labels. like this:

List1=[Images,Labels]

For example, List1 is a list with 700 images with label 0. List2 is a list with 1000 images with label 1, ... Hence, we have a list of 50 lists in which each individual list comes with size 2.

I want to merge all list together in order to get the following matrix. I mean an array like this:

dataTest=[Images of List1,2,3,...,50  , Labels of List1,2,3,...,50]

So, we would have a list with two size. The first dimension is all images from all lists, and the second dimension is the labels of all images

Either that, or you want dataTest=sum(dataTest,[]), can't really tell. — NightShadeQueen
– NightShadeQueen, Commented Jul 17, 2015 at 5:17
Your result matrix is missing commas or some other syntax, so it's hard to tell what you actually are asking. — John La Rooy
– John La Rooy, Commented Jul 17, 2015 at 5:33
Working with lists of lists of lists gets very cumbersome, I'd look for an easier to use datatype if I were you. Please don't use the word "dimension" because it makes it seem like you're using multi-dimensional arrays (which lists of lists are not). — RemcoGerlich
– RemcoGerlich, Commented Jul 17, 2015 at 9:58

The6thSense · Accepted Answer · 2015-07-17 05:54:44Z

1

Is this what you want:

a=[[1,2],[2,3]]
[v for d in a for v in d]
[1, 2, 2, 3]

Changed after OP's edit:

a=[[2,3],[2,3]]
c=[]
c.append([v[0] for v in a])
c.append([v[1] for v in a])
print c
[[2, 2], [3, 3]]

edited Jul 17, 2015 at 5:54

answered Jul 17, 2015 at 5:17

The6thSense

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7 Comments

akh Over a year ago

I want somethong like this: [[1,2] in a row, and [2,3]] in another row

The6thSense Over a year ago

@akh isn't your data already like that ! do you want to iterate over list1 to list50 and append it to dataset

akh Over a year ago

I have 10000 images that I reshape them into a row. They are in different labels. I divided them based on their labels, and called List1,2, ...,50. Now I want to merge them sequentially. I mean, I want an array of all of them.

The6thSense Over a year ago

@akh it is really confusing of what you are asking can you provide same input and sample output which is more explanatory then the previous one

akh Over a year ago

@VigneshKalai, I can use 'zip(*)' to find what you say. It provides a list of the lists. What I want is to separate all lists, and then merge together. May be an image from a list come after that an image from another list.

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mstuebner · Accepted Answer · 2015-07-17 06:31:30Z

If I got it right, then the data "List1=[Images,Labels]" has the structure that Images is a list of images and Labels is a list of labels? If that is true, the code below merges them and generates a resulting list which holds a list (or better a tuple, but that can of course be converted) of all images and a list of all labels:

    # generate sample data
    l1 = [['IMG_1', 'IMG_2', 'IMG_3', 'IMG_4'],['IMG_LABEL_1', 'IMG_LABEL_2', 'IMG_LABEL_3', 'IMG_LABEL_4']]
    l2 = [['IMG_11', 'IMG_12', 'IMG_13', 'IMG_14'],['IMG_LABEL_11', 'IMG_LABEL_12', 'IMG_LABEL_13', 'IMG_LABEL_14']]
    l3 = [['IMG_21', 'IMG_22', 'IMG_23', 'IMG_24'],['IMG_LABEL_21', 'IMG_LABEL_22', 'IMG_LABEL_23', 'IMG_LABEL_24']]
    data = [l1, l2, l3]

    merged_list = []

    # merge the lists
    for source_list in data:
        merged_list += zip(source_list[0], source_list[1])

    # change its structure
    result_list = zip(*merged_list)

Results in:

    [
    ('IMG_1', 'IMG_2', 'IMG_3', 'IMG_4', 'IMG_11', 'IMG_12', 'IMG_13', 'IMG_14', 'IMG_21', 'IMG_22', 'IMG_23', 'IMG_24'), 
    ('IMG_LABEL_1', 'IMG_LABEL_2', 'IMG_LABEL_3', 'IMG_LABEL_4', 'IMG_LABEL_11', 'IMG_LABEL_12', 'IMG_LABEL_13', 'IMG_LABEL_14', 'IMG_LABEL_21', 'IMG_LABEL_22', 'IMG_LABEL_23', 'IMG_LABEL_24')
    ]

NightShadeQueen · Accepted Answer · 2015-07-17 05:21:06Z

0

If flattening a list is what you're trying to do, you can just sum the lists together.

dataTest=sum(dataTest,[])

answered Jul 17, 2015 at 5:21

NightShadeQueen

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2 Comments

The6thSense Over a year ago

Could you add sample input and output

John La Rooy Over a year ago

Please don't recommend this. Using sum with lists has quadratic performance.

ajsp · Accepted Answer · 2015-07-17 05:30:27Z

0

You just need to flatten the list by the looks of things, you can do so with itertools

from itertools import*
dataTest=[['a',1],['a',2],['a',3]]
print [k for k in chain.from_iterable(k[0] for k in dataTest)]

Output

['a', 'a', 'a']

edited Jul 17, 2015 at 5:30

answered Jul 17, 2015 at 5:17

ajsp

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3 Comments

akh Over a year ago

Actually I want to add all images from all lists together in an array. Foe example, if the number of images in all lists are 10000, I want to have an array with 10000 images

ajsp Over a year ago

Ah I see, the answer has been updated. Let me know if you're ok.

belteshazzar Over a year ago

import * is a bad idea. Always import the exact thing you want to use.

Martin Evans · Accepted Answer · 2015-07-17 09:27:59Z

I have created a dataTest hopefully in the same format as you have:

List1 = [["img11", "img12", "img13"], ["label11", "label12", "label13", "label14"]]
List2 = [["img21", "img22", "img23"], ["label21", "label22", "label23", "label24"]]
List3 = [["img31", "img32", "img33"], ["label31", "label32", "label33", "label34"]]

dataTest = [List1, List2, List3]

print "Input:", dataTest
print

dataTest2 = [[],[]]

for cur_list in dataTest:
    dataTest2[0].extend(cur_list[0])
    dataTest2[1].extend(cur_list[1])

print "Output:", dataTest2

This produces a list with 2 elements, the first containing all of the images, and the second containing all of the labels:

Input: [[['img11', 'img12', 'img13'], ['label11', 'label12', 'label13', 'label14']], [['img21', 'img22', 'img23'], ['label21', 'label22', 'label23', 'label24']], [['img31', 'img32', 'img33'], ['label31', 'label32', 'label33', 'label34']]]

Output: [['img11', 'img12', 'img13', 'img21', 'img22', 'img23', 'img31', 'img32', 'img33'], ['label11', 'label12', 'label13', 'label14', 'label21', 'label22', 'label23', 'label24', 'label31', 'label32', 'label33', 'label34']]

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