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Simple array operations
Those of you who use (have used) Origin are you used to doing simple manipulation of datasets with the embedded spreadsheet functionality. Selecting data, only using every nth datapoint etc. are capabilities that we need all the time. This short tutorial will introduce a few array manipulations in Python. A more substantial introduction can be found at the numpy tutorial page. There are also two excellent video tutorials that I highly recommend watching on array indexing by Enthought can be viewed here and here.
First, let’s create a couple of datasets.
one_d = numpy.linspace(0,100,100)
two_d = numpy.zeros((len(one_d),2))
two_d[:,0] = one_d
two_d[:,1] = one_d**3 + 14.5*2
Selecting points from 5th row onwards in 1-d array. Remember, Python indexes from 0.
ew_array = one_d[4:]
Selecting points from 5th row onwards in 2-d array.
new_array = two_d[4:,:]
Selecting every 2nd point in the 1-d array.
new_array = one_d[::2]
Selecting every 2nd point in the 2-d array.
new_array = two_d[::2,:]
Remove the last 5 points from the 1-d array.
new_array = one_d[:-5]
Sorting is usually trivial in numpy with the sort command.
Sort y according to x in the 2-d array.
indices = numpy.argsort(two_d[:,0])
x = two_d[:,0]
new_x = x[indices]
y = two_d[:,1]
new_y = y[indices]
two_d[:,0] = new_x
two_d[:,1] = new_y
Selecting x values such that (20 < x <67) and the corresponding y values.
x = two_d[:,0]
y = two_d[:,1]
index = (x>20) & (x<67)
new_x = x[index]
new_y = y[index]
That’s all for now, folks! Drop me a line via the suggestion box or email MESA (firstname.lastname@example.org) if you have any questions or requests.
Post contributed by Shrividya Ravi, VUW
LabVIEW Basics Workshop
Always wanted to learn a little more about building LabVIEW programmes? This 1-2 hour workshop, with Victoria University’s Dr. Howard Lukefahr, will gently introduce you to the basics of creating a LabVIEW program for interacting with lab equipment, plotting, analysing data and signal processing.
No prior programming experience is necessary!
Spaces are still available for the free event, email email@example.com to sign up, or show up on the day.
Tuesday 14th May 2013, 5.30pm. Location: Laby 203, VUW (Wellington)
Alumni & Members: Join the MacDiarmid LinkedIn GroupMESA and the MacDiarmid Institute would like to invite you to connect to our official LinkedIn group, host to all of the Institute's members and alumni. These include many of New Zealand's leading researchers in nanotechnology and materials science, plus alumni pursuing careers abroad. Join us to network with current and former MacDiarmid researchers!
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