Histogram of Query Results

[francbelf]

This is not a bug, but rather a functionality request. I want to be able to do a spaxel query and then histogram the results. For example

from marvin.tools.query import doQuery
q, r = doQuery(searchfilter='nsa.sersic_logmass >= 10 and nsa.sersic_logmass <= 11', returnparams='emline_gflux_ha_6564')
df = r.toDF()

now I want to plot a histogram of df, but unfortunately df only contains the first 100 spaxels. How can I get all of the them in an easy way?

[bretthandrews]

@francbelf Returning all of the spaxels from a large query would be very expensive, but it might be possible to calculate the histogram on the server side and return just the histogram. Would that work for your use case?

[francbelf]

Hi Brett, I opened this issue after talking about it with Brian at JHU last week. Basically, I love the spaxel query capabilities of Marvin, but so far I have struggled to use them because after I run the query, I can’t access the results! Histograms is just one example. The reason I want to do the query is because I want it to return an array of numbers that I can manipulate, analyse and explore. I can’t do that with the first N samples, I need the whole thing. Maybe it’s worth expanding on the use case I had in mind. We have had a lot of discussion on the DAP on whether to tie the sigmas of different emission lines. What I wanted to do was to use marvin to do a query for spaxels with S/N>3 on Ha and [OIII], return two (admittedly long) arrays of sigma_Ha and sigma_OIII for these spaxels and do a histogram of sigma_Ha/sigma_OIII. So I think what I would like is a functionality that would allow me to export a whole array of returned properties (say sigma_Ha and sigma_OIII in the example I gave) into my local machine. This particular query resulted in 10^7 spaxels, so in my particular use case I would get two arrays of length 10^7. I guess these are large numbers, but they sounds reasonable to me (for example they are comparable to a 127-fibre datacube). Let me know if I am missing something on how to correctly interact with the query results! Best, F.

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---------------------------------------------------------------------------- Francesco Belfiore Astrophysics Group and Kavli Institute for Cosmology, Cavendish Laboratory, Cambridge, CB3 0HE, United Kingdom & University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, Mailstop: UCO/Lick, USA On 21 May 2017, at 13:53, Brett Andrews <notifications@github.com<mailto:notifications@github.com>> wrote: @francbelf<https://github.com/francbelf> Returning all of the spaxels from a large query would be very expensive, but it might be possible to calculate the histogram on the server side and return just the histogram. Would that work for your use case? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub<#263 (comment)>, or mute the thread<https://github.com/notifications/unsubscribe-auth/ATS2C8dL4tveB0H0sgieVfAfOBvOe-kgks5r8KRTgaJpZM4Nheuj>.

[havok2063]

Added in MPL6 release