On 12/14/2011 05:20 PM, Eric wrote:
I'm trying to read some file data into a set of arrays. The file data
is just four columns of numbers, like so:
1.2 2.2 3.3 0.5
0.1 0.2 1.0 10.1
... and so on
I'd like to read this into four arrays, one array for each column.
Alternatively, I guess something like this is okay too:
[[1.2, 2.2, 3.3, 0.5], [0.1, 0.2, 1.0, 10.1], ... and so on]
I came up with the following for the four array option:
file = open(fileName, 'r')
for line in file.readlines():
The readlines() call is a waste of time/space. file is already an
iterator that'll return lines for you.
d1, e1, d2, e2 = map(float, line.split())
data1.append(d1) # where data1, err1, data2, err2 are init-ed
as empty lists
err1.append(e1)
data2.append(d2)
err2.append(e2)
file.close()
But somehow it doesn't seem very python-esque (I'm thinking there's a
more elegant and succinct way to do it in python). I've also tried
replacing the above "map" line with:
d = d + map(float, line.split()) # where d is initialized as d
= []
But all I get is one long flat list, not what I want.
So is the map and append method the best I can do or is there a
slicker way?
One more thing, no numpy. Nothing against numpy but I'm curious to
see what can be done with just the box stock python install.
TIA,
eric
When I see a problem like this, I turn to zip(). It's got some powerful
uses when rows and columns need inverting.
I didn't try it on an actual file, but the following works:
linedata = [[1.2, 2.2, 3.3, 0.5], [0.1, 0.2, 1.0, 10.1] ]
data, err1, data2, err2 = zip(*linedata)
print data
print err1
print data2
print err2
So you could try (untested)
file = open(filename, "r")
linedata = [ map(float, line) for line in file]
data, err1, data2, err2 = zip(*linedata)
file.close()
Note that your code won't work (and mine probably won't either) if one
of the lines has 3 or 5 items. Or if one of the numbers isn't legal
format for a float. So you need to think about error checking, or
decide whether a partial result is important.
--
DaveA
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