Trying to create an array of x and y values after reading file in Python

Question

Initially I was simply using MatPlotLib to graph the points after I read them like this:

with open("data1.txt") as f:
    samples = f.read()

samples = samples.split('\n')

x = [row.split(' ')[0] for row in samples]
y = [row.split(' ')[1] for row in samples]

fig = plt.figure()

ax1 = fig.add_subplot(111)

ax1.plot(x,y, 'ro')

However, I now realize I need to store all that information in an array of some kind to be used later. I'm new to python, so I'm wondering either how I could access these points individually if my samples variable already has what I want, or instead create a new array or list to store all my x and y values easily.

EDIT:

This is how my txt file looks:
0.1394 0.8231
1.2149 1.8136
1.3823 0.8263
1.3726 0.8158
1.3694 0.8158
1.3855 0.8123
1.3919 0.8053
1.3694 0.8123
1.3661 0.8123
1.3597 0.7982
1.3565 0.6061
1.3468 0.7126
1.3823 0.7494

Are you looking for something of the sort [(x1,y1),(x2,y2),.....] ? — nitimalh
– nitimalh, Commented Feb 7, 2015 at 22:46
Yea exactly like that, so I guess a double array would be better then? I'm still not sure how I would do that though. — Ganda
– Ganda, Commented Feb 7, 2015 at 22:51

Padraic Cunningham · Accepted Answer · 2015-02-07 22:57:11Z

1

If you only have have the x and y just add them in one list comp:

with open("data1.txt") as f:
    coords = [line.split() for line in f]

print(coords)
[['0.1394', '0.8231'], ['1.2149', '1.8136'], ['1.3823', '0.8263'], ['1.3726', '0.8158'], ['1.3694', '0.8158'], ['1.3855', '0.8123'], ['1.3919', '0.8053'], ['1.3694', '0.8123'], ['1.3661', '0.8123'], ['1.3597', '0.7982'], ['1.3565', '0.6061'], ['1.3468', '0.7126'], ['1.3823', '0.7494']]

To get floats use coords = [list(map(float,line.split())) for line in f]

[[0.1394, 0.8231], [1.2149, 1.8136], [1.3823, 0.8263], [1.3726, 0.8158], [1.3694, 0.8158], [1.3855, 0.8123], [1.3919, 0.8053], [1.3694, 0.8123], [1.3661, 0.8123], [1.3597, 0.7982], [1.3565, 0.6061], [1.3468, 0.7126], [1.3823, 0.7494]]

You don't need to create two lists and then zip, just do it when your read from the file.

edited Feb 7, 2015 at 22:57

answered Feb 7, 2015 at 22:51

Padraic Cunningham

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5 Comments

Ganda Over a year ago

This worked. I'm used to java in that I could just call coords in a format like x = coords[0] or something like that to get the 0th term in the list. What would be the syntax for that now that I have this coords list?

Padraic Cunningham Over a year ago

if you want the first element just use the same idea, your_list[0] will get the first subelement, your_list[1] will get the second etc

Ganda Over a year ago

So if I called coords[0], would that return me just 0.1394 or 0.1394 and 0.8321. I just tested and it return both. How could I access just one of the values?

Padraic Cunningham Over a year ago

0.1394, 0.8231 if you wanted just x it would be your_list[0][0] access the subelement of the sublist

Padraic Cunningham Over a year ago

To transpose the list print(list(zip(*coords)))

nitimalh · Accepted Answer · 2015-02-07 22:51:35Z

0

This is how you could easily achieve it since you already have the x and y points:

a = [1,2,3]
b = [4,5,6]
print zip(a,b)

output : [(1, 4), (2, 5), (3, 6)]

answered Feb 7, 2015 at 22:51

nitimalh

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Comments

Joran Beasley · Accepted Answer · 2015-02-07 22:55:54Z

0

there is a great grouper recipe

samples = samples.split() #split on all whitespace [x1,y1,x2,y2,...]
#you may want to map to int with `map(int,samples)`
coordinates = zip(*[iter(samples)]*2) #group by twos [(x1,y1),(x2,y2),...]
x,y = zip(*coordinates) # x= [x1,x2,...] ; y = [y1,y2,...]

edited Feb 7, 2015 at 22:55

answered Feb 7, 2015 at 22:48

Joran Beasley

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