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Resampling with Pandas
The first counts all the rows from each 20 minute slot In [11]: df1.IP.resample('20t', how='count') # I usually prefer '20min' Out[11]: datetime 2013-05-30 06:00:00 3 2013-05-30 06:20:00 1 dtype: int64 The second grabs those rows between certain times: In [12]: df1.IP.between_time('06:00:00', '06:20:00') Out[12]: datetime 2013-05-30 06:00:41 2013-05-30 06:05:41 2013-05-30 06:10:42 Name: IP, dtype: object There may to be a neat solution to the general problem (so you don't need to specify the times between) using a TimeGrouper, but this is the best I can do, to print all of the groupings: In [13]: tg = pd.TimeGrouper('20t') In [14]: g = df1.groupby(tg) In [15]: def f(x): print x return x In [

Categories : Python

resampling or interpolation?
There are some relationships between interpolation and resampling. Resampling implies changing the sample rate of a set of samples. In the case of an image, these are the pixel values sampled at each pixel coordinate in the image. In the case of audio, these are the amplitude values sampled at each time point. Resampling is used to either increase the sample rate (make the image larger) or decrease it (make the image smaller). Interpolation is the process of calculating values between sample points. So, if you resample an image you can use interpolation to do it. There are a lot of interpolation methods - nearest neighbor, linear, cubic, lanczos etc. Each method has different quality/performance. If you reduce the sampling rate, you can get aliasing. This is where you are trying t

Categories : Misc

Resampling Audio in MATLAB
Yes, resample is your function. To downsample x from 44100 Hz to 22050 Hz: y = resample(x,1,2); (the "1" and "2" arguments define the resampling ratio: 22050/44100 = 1/2) To upsample back to 44100 Hz: x2 = resample(y,2,1); Note that the resample function includes the necessary anti-aliasing (lowpass) filter. As you probably know, the "recovered" signal x2 has lost the highest-frequency information that may have been present in x.

Categories : Matlab

Resizing a 3D image (and resampling)
From the docstring for scipy.ndimage.interpolate.zoom: """ zoom : float or sequence, optional The zoom factor along the axes. If a float, `zoom` is the same for each axis. If a sequence, `zoom` should contain one value for each axis. """ What is the scale factor between the two images? Is it constant across all axes (i.e. are you scaling isometrically)? In that case zoom should be a single float value. Otherwise it should be a sequence of floats, one per axis. For example, if the physical dimensions of whole and flash can be assumed to be equal, then you could do something like this: dsfactor = [w/float(f) for w,f in zip(whole.shape, flash.shape)] downed = nd.interpolation.zoom(flash, zoom=dsfactor)

Categories : Python

Resampling Image using JMagick
It appears there are no convenience methods for both -resample and -layers options. The only thing in JMagick's API docs that resembles any of those options is the method sampleImage in class MagickImage. However, that operates only in pixels. There is indeed a setUnits method that allows you to change the units declared in the header of the image file. But that's about it. It doesn't modify the image itself. And there seems to be no connection between the sampleImage and setUnits methods. There is some code out there to resample an image using "manual" calculations. The following snippet is based on the one available here: MagickImage lightImg = new MagickImage (new ImageInfo (strOrigPath)); //Get the original resolution double origXRes = lightImg.getXResolution(); double origYRes

Categories : Java

R: Row resampling loop speed improvement
I put very little thought into actually optimizing this, I was just concentrating on doing something that's at least reasonable while matching your procedure. Your big problem is that you are growing objects via rbind and cbind. Basically anytime you see someone write data.frame() or c() and expand that object using rbind, cbind or c, you can be very sure that the resulting code will essentially be the slowest possible way of doing what ever task is being attempted. This version is around 12-13 times faster, and I'm sure you could squeeze some more out of this if you put some real thought into it: s_size <- 200 int <- 10 reps <- 30 ss <- rep(seq(1,s_size,by = int),each = reps) id <- rep(seq_len(reps),times = s_size/int) foo <- function(i,j,data){ res <- data[s

Categories : R

Strange behavior of pandas resampling
Perhaps you want interpolate instead of resample. Here's one way: In [53]: index = pd.date_range(freq='66T', start=ts.first_valid_index(), periods=5) In [54]: ts.reindex(set(ts.index).union(index)).sort_index().interpolate('time').ix[index] Out[54]: 2011-01-02 01:00:00 0.0 2011-01-02 02:06:00 1.1 2011-01-02 03:12:00 2.2 2011-01-02 04:18:00 3.3 2011-01-02 05:24:00 4.4 Freq: 66T, dtype: float64 In [55]: index = pd.date_range(freq='65T', start=ts.first_valid_index(), periods=5) In [56]: ts.reindex(set(ts.index).union(index)).sort_index().interpolate('time').ix[index] Out[56]: 2011-01-02 01:00:00 0.000000 2011-01-02 02:05:00 1.083333 2011-01-02 03:10:00 2.166667 2011-01-02 04:15:00 3.250000 2011-01-02 05:20:00 4.333333 Freq: 65T, dtype: float64 That said,

Categories : Python

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