# Difference between allowrankdeficient and dropcollinear in lm function

**URL:** <https://discourse.julialang.org/t/difference-between-allowrankdeficient-and-dropcollinear-in-lm-function/86047>\
**Category:** General Usage\
**Tags:** package, argument, glm\
**Created:** [August 20, 2022, 1:27am UTC](https://discourse.julialang.org/t/difference-between-allowrankdeficient-and-dropcollinear-in-lm-function/86047 "2022-08-20T01:27:45Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![valperez](https://avatars.discourse-cdn.com/v4/letter/v/e79b87/32.png) [@valperez](https://discourse.julialang.org/u/valperez)\
**Post date:** [August 20, 2022, 1:27am UTC](https://discourse.julialang.org/t/difference-between-allowrankdeficient-and-dropcollinear-in-lm-function/86047/1 "2022-08-20T01:27:45Z")

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Hi there!

I have a question regarding the documentation of the GLM package. I want to use the function

> lm(formula, data, allowrankdeficient=false;  
> [wts::AbstractVector], dropcollinear::Bool=true)

but I have a doubt about the difference between the “allowrankdeficient” and “dropcollinear” arguments. They seem to do the same job so I can’t tell them apart. Could someone give me more insight?

Thank you in advance!

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**Author:** ![rafael.guerra](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rafael.guerra/32/216610_2.png) [@rafael.guerra](https://discourse.julialang.org/u/rafael.guerra)\
**Post date:** [August 20, 2022, 8:18am UTC](https://discourse.julialang.org/t/difference-between-allowrankdeficient-and-dropcollinear-in-lm-function/86047/2 "2022-08-20T08:18:02Z")

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Searching the github repository, shows in GLM.jl/test/runtests.jl :

Positional argument `allowrankdeficient` is deprecated, use keyword argument `dropcollinear` instead.

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<div class="post-metadata">

**Author:** ![valperez](https://avatars.discourse-cdn.com/v4/letter/v/e79b87/32.png) [@valperez](https://discourse.julialang.org/u/valperez)\
**Post date:** [August 21, 2022, 6:44pm UTC](https://discourse.julialang.org/t/difference-between-allowrankdeficient-and-dropcollinear-in-lm-function/86047/3 "2022-08-21T18:44:04Z")

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Yo are right! Thank you so much