I need to read in a text file with data into python and assign the data the variables

Question

The data in the file looks like this; two columns that need to represent X and Y values. The first value in the will be X values and second value will be Y values.

   42.10      8.55
   40.25      7.60
   38.50      8.95
   39.55      6.45
   40.90      7.75

I need to read it into python and assign variables to each set of values in each line: for example, (42.10,8.55) where 42.10 is the x value and 8.55 is the y value. There are several lines of values that need this kind of organization. I can open the file and read it in however I can't get the variable assignments I want.

so far I have

with open ("file.txt", "r") as myfile:
    data=myfile.read().split()

Ok, so now here's where I'm at now:

with open('file.txt') as f:
    data = [line.split() for line in f.readlines()]
    out = [(float(x), float(y)) for x, y in data]
for i in out:
   print i

I want to create a scatter plot of the data in the for Loop, which module would you recommend?

show us what you have for opening the file and reading it in, and clarify what you mean for getting the variable assignments you want. — mhlester, Mar 05 '14 at 23:28
with open ("file.txt", "r") as myfile: data=myfile.read().split() — Astronerd326, Mar 05 '14 at 23:32
Is your data two numbers in a line like this: `1 2` (next line) `3 4` or a single line of numbers? When you say `The larger numbers will be X values and smaller numbers will be Y` does that mean the larger of the two numbers read? This is very unclear... — dawg, Mar 05 '14 at 23:33
dawg, it's just like I have posted in the example above. The column beginning with 42.10 will be the X coordinates and the column beginning with 8.55 will be the Y coordinates. so the first position will be (42.10,8.55) — Astronerd326, Mar 05 '14 at 23:56
see my last comment below, there is a link to what you want, but you need to get the module matplotlib — Totem, Mar 06 '14 at 00:48
~I would make the plot question into a whole new question if I was you — Totem, Mar 06 '14 at 00:49
I have matplotlib on my home PC so I'm set there. I looked at the link you shared and it seems very helpful, I'm just not familiar with the zip(*) call in the code so I'll do some research on that. If i run into trouble I'll create a new question for plotting it. — Astronerd326, Mar 06 '14 at 00:56

PyNEwbie · Answer 1 · 2014-03-06T01:58:32.313

3

data = []
for line in open(myfile).readlines():
       temp_x,temp_y = line.split()
       x = float(temp_x)
       y = float(temp_y)
       data.append((x,y))

You can get fancier, but this is all you need to get started.

The reason you only get the most recent values of x and y is because x and y change their values with each iteration of the loop. To see all of the values

for each_pair in data:
    (x, y) = each_pair
    print 'X = ',x, 'Y = ', y

edited Mar 06 '14 at 01:58

answered Mar 05 '14 at 23:34

PyNEwbie

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I'm more concerned about the concept as opposed to "beauty" right now, thank you PyNEwbie. – Astronerd326 Mar 05 '14 at 23:41
alright I have a question to follow up the code. when i print x and print y it gives me the values for the first row of numbers. What do I need to do to have the remaining x and y values returned? – Astronerd326 Mar 05 '14 at 23:52

Totem · Accepted Answer · 2014-03-05T23:54:15.160

1

data and out are constructed here with list comprehensions:

with open('text.txt') as f:
    data = [line.split() for line in f.readlines()]
    out = [(float(k), float(v)) for k, v in data]

output:

for i in out:
    print i

(42.1, 8.55)
(40.25, 7.6)
(38.5, 8.95)
(39.55, 6.45)
(40.9, 7.75)

You can assign these to variables if you want, or you could reference them with out[0] etc.

How you go about naming them all depends on how many you have, but here is an example anyhow:

>>> first_tuple = out[0] 
>>> print first_tuple
(42.1, 8.55)

edited Mar 05 '14 at 23:54

answered Mar 05 '14 at 23:41

Totem

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this is great, this is what I was working towards! I couldn't for the life of me get the two columns to pair rows. – Astronerd326 Mar 05 '14 at 23:59
Totem, now that I have Coordinates could I replace print i with plot i? Basically I want to create a scatter plot with the coordinates. – Astronerd326 Mar 06 '14 at 00:04
when you say plot, what do you mean exactly? Are you using any particular module etc for creating graphs? – Totem Mar 06 '14 at 00:16
as far as plotting goes I'd like to use numpy and pylab to create a scatter plot.And when I say plot I mean I have 50 sets of coordinates which you just helped me set up. So I'd want to plot a point at (42.1,8.55) another at (40.25,7.6)...etc as the set of coordinates in the "print i" appears – Astronerd326 Mar 06 '14 at 00:33
well yes, I would say that's very doable with the for loop instead of print. However, I am not so familiar with numbpy and pylab, so I would google that or search the site if I was you. Maybe cast another question specifically for this as it goes beyond the scope of your original question – Totem Mar 06 '14 at 00:35
Great thank you! So with the for loop constructed above I will use the plot procedure instead of print. do you have any recomendations for a module I could use to create a scatter plot with the data in the for loop? – Astronerd326 Mar 06 '14 at 00:40
I believe matplotlib is a module for graphs etc. I don't know exactly how it would work with a for loop to plot your graph, it might even be simpler than that. I would check that out. maybe start here: http://stackoverflow.com/questions/17478779/make-scatter-plot-from-set-of-points-in-tuples – Totem Mar 06 '14 at 00:45
When I return to my home computer I will give it a go with matplotlib. I'm very new to python and still trying to figure out which modules are best suited for particular situations. Thanks again Totem. – Astronerd326 Mar 06 '14 at 00:50

I need to read in a text file with data into python and assign the data the variables

2 Answers2