CODEWITHSUNDEEP
pythonlistastropy
Jacob
Jacob

Reputation: 103

Getting rid of empty elements in a list

I am working with astropy and I am at a point where I printed Data and got the following result as my output:

[<MaskedColumn name='phot_bp_rp_excess_factor' dtype='float32' description='BP/RP excess factor' length=1>
4.678),                                       
(<MaskedColumn name='phot_bp_rp_excess_factor' dtype='float32' description='BP/RP excess factor' length=0>], 
(<MaskedColumn name='phot_bp_rp_excess_factor' dtype='float32' description='BP/RP excess factor' length=1>
9.876)]

So now I am trying to put "BP/RP excess factor" in a new list x, so I tried:

x=[]
for i in data:  
    if bp > 0:
    x.append(bp[-1]) # "[-1]" to get rid of text and just print out the numbers 
#I am expecting [4.678,9.876]

But this gives me an error saying index -1 is out of bounds for axis 0 with size 0. I know this problems exist because in my output above I have length=0, but I dont know to write a code that ignores if "length=0" and gives me a list of numbers for elements that have "length=1".

Upvotes: 0

Views: 55

Answers (1)

Josh Smeaton
Josh Smeaton

Reputation: 48710

I'm not familiar with astropy, but filtering on the length of data seems to work in my local testing:

from astropy.table import MaskedColumn

In [16]: columns = [
    ...:     MaskedColumn(data=[1]),
    ...:     MaskedColumn(data=[]),
    ...:     MaskedColumn(data=[2,3])
    ...: ]

In [17]: not_empty = [col for col in columns if len(col.data) > 0]

In [18]: not_empty
Out[18]:
[<MaskedColumn dtype='int64' length=1>
 1,
 <MaskedColumn dtype='int64' length=2>
 2
 3]

In [19]: len(not_empty)
Out[19]: 2

Edit:

column.size also works, thanks to @python_user in the comments:

not_empty = [col for col in columns if col.size > 0]

Upvotes: 1

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