Thomas Matthew - 6 months ago 33

Python Question

Is there a graphing library for python that doesn't require storing all raw data points as a

`numpy`

I have a dataset

What I'm looking for is a library that can take the output of a generator (each data point yielded from a file, as a

`float`

This includes computing bin size as the generator yields each data point from the file.

`numpy`

`{bin_1:count_1, bin_2:count_2...bin_x:count_x}`

Datapoints are held as a vertical matrix, in a tab file, arranged by

`node-node-score`

`node node 5.55555`

- 104301133 lines in data (so far)
- I don't know the min or max values
- bin widths should be the the same
- number of bins could be 1000

`low = np.inf`

high = -np.inf

# find the overall min/max

chunksize = 1000

loop = 0

for chunk in pd.read_table('gsl_test_1.txt', header=None, chunksize=chunksize, delimiter='\t'):

low = np.minimum(chunk.iloc[:, 2].min(), low)

high = np.maximum(chunk.iloc[:, 2].max(), high)

loop += 1

lines = loop*chunksize

nbins = math.ceil(math.sqrt(lines))

bin_edges = np.linspace(low, high, nbins + 1)

total = np.zeros(nbins, np.int64) # np.ndarray filled with np.uint32 zeros, CHANGED TO int64

# iterate over your dataset in chunks of 1000 lines (increase or decrease this

# according to how much you can hold in memory)

for chunk in pd.read_table('gsl_test_1.txt', header=None, chunksize=2, delimiter='\t'):

# compute bin counts over the 3rd column

subtotal, e = np.histogram(chunk.iloc[:, 2], bins=bin_edges) # np.ndarray filled with np.int64

# accumulate bin counts over chunks

total += subtotal

plt.hist(bin_edges[:-1], bins=bin_edges, weights=total)

# plt.bar(np.arange(total.shape[0]), total, width=1)

plt.savefig('gsl_test_hist.svg')

Answer

You could iterate over chunks of your dataset and use `np.histogram`

to accumulate your bin counts into a single vector (you would need to define your bin edges a priori and pass them to `np.histogram`

using the `bins=`

parameter), e.g.:

```
import numpy as np
import pandas as pd
bin_edges = np.linspace(low, high, nbins + 1)
total = np.zeros(nbins, np.uint)
# iterate over your dataset in chunks of 1000 lines (increase or decrease this
# according to how much you can hold in memory)
for chunk in pd.read_table('/path/to/my/dataset.txt', header=None, chunksize=1000):
# compute bin counts over the 3rd column
subtotal, e = np.histogram(chunk.iloc[:, 2], bins=bin_edges)
# accumulate bin counts over chunks
total += subtotal.astype(np.uint)
```

If you want to ensure that your bins span the full range of values in your array, but you don't already know the minimum and maximum then you will need to loop over it once beforehand to compute these (e.g. using `np.min`

/`np.max`

), for example:

```
low = np.inf
high = -np.inf
# find the overall min/max
for chunk in pd.read_table('/path/to/my/dataset.txt', header=None, chunksize=1000):
low = np.minimum(chunk.iloc[:, 2].min(), low)
high = np.maximum(chunk.iloc[:, 2].max(), high)
```

Once you have your array of bin counts, you can then generate a bar plot directly using `plt.bar`

:

```
plt.bar(bin_edges[:-1], total, width=1)
```

It's also possible to use the `weights=`

parameter to `plt.hist`

in order to generate a histogram from a vector of counts rather than samples, e.g.:

```
plt.hist(bin_edges[:-1], bins=bin_edges, weights=total, ...)
```