[ https://issues.apache.org/jira/browse/SPARK5089?page=com.atlassian.jira.plugin.system.issuetabpanels:alltabpanel
]
Jeremy Freeman updated SPARK5089:

Description:
Prior to performing many MLlib operations in PySpark (e.g. KMeans), data are automatically
converted to `DenseVectors`. If the data are numpy arrays with dtype `float64` this works.
If data are numpy arrays with lower precision (e.g. `float16` or `float32`), they should be
upcast to `float64`, but due to a small bug in this line this currently doesn't happen (casting
is not inplace).
``
if ar.dtype != np.float64:
ar.astype(np.float64)
``
Nonfloat64 values are in turn mangled during SerDe. This can have significant consequences.
For example, the following yields confusing and erroneous results:
```
from numpy import random
from pyspark.mllib.clustering import KMeans
data = sc.parallelize(random.randn(100,10).astype('float32'))
model = KMeans.train(data, k=3)
len(model.centers[0])
>> 5 # should be 10!
```
But this works fine:
```
data = sc.parallelize(random.randn(100,10).astype('float64'))
model = KMeans.train(data, k=3)
len(model.centers[0])
>> 10 # this is correct
```
The fix is trivial, I'll submit a PR shortly.
was:
Prior to performing many MLlib operations in PySpark (e.g. KMeans), data are automatically
converted to `DenseVectors`. If the data are numpy arrays with dtype `float64` this works.
If data are numpy arrays with lower precision (e.g. `float16` or `float32`), they should be
upcast to `float64`, but due to a small bug in this line this currently doesn't happen (casting
is not inplace).
```
if ar.dtype != np.float64:
ar.astype(np.float64)
```
Nonfloat64 values are in turn mangled during SerDe. This can have significant consequences.
For example, the following yields confusing and erroneous results:
```
from numpy import random
from pyspark.mllib.clustering import KMeans
data = sc.parallelize(random.randn(100,10).astype('float32'))
model = KMeans.train(data, k=3)
len(model.centers[0])
>> 5 # should be 10!
```
But this works fine:
```
data = sc.parallelize(random.randn(100,10).astype('float64'))
model = KMeans.train(data, k=3)
len(model.centers[0])
>> 10 # this is correct
```
The fix is trivial, I'll submit a PR shortly.
> Vector conversion broken for nonfloat64 arrays
> 
>
> Key: SPARK5089
> URL: https://issues.apache.org/jira/browse/SPARK5089
> Project: Spark
> Issue Type: Bug
> Components: MLlib, PySpark
> Affects Versions: 1.2.0
> Reporter: Jeremy Freeman
>
> Prior to performing many MLlib operations in PySpark (e.g. KMeans), data are automatically
converted to `DenseVectors`. If the data are numpy arrays with dtype `float64` this works.
If data are numpy arrays with lower precision (e.g. `float16` or `float32`), they should be
upcast to `float64`, but due to a small bug in this line this currently doesn't happen (casting
is not inplace).
> ``
> if ar.dtype != np.float64:
> ar.astype(np.float64)
> ``
>
> Nonfloat64 values are in turn mangled during SerDe. This can have significant consequences.
For example, the following yields confusing and erroneous results:
> ```
> from numpy import random
> from pyspark.mllib.clustering import KMeans
> data = sc.parallelize(random.randn(100,10).astype('float32'))
> model = KMeans.train(data, k=3)
> len(model.centers[0])
> >> 5 # should be 10!
> ```
> But this works fine:
> ```
> data = sc.parallelize(random.randn(100,10).astype('float64'))
> model = KMeans.train(data, k=3)
> len(model.centers[0])
> >> 10 # this is correct
> ```
> The fix is trivial, I'll submit a PR shortly.

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