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Questions tagged [poly]

Poly is a function in R that generates a basis matrix of polynomial transformations.

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Why does lm() with the subset argument give a different answer than subsetting in advance?

I am using lm() on a training set of data that includes a polynomial. When I subset in advance with [ ] I get different coefficients compared to using the subset argument in the lm() function call. Why? library(ISLR2) set.seed (1) train <-…
itsMeInMiami
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How to include a spatial lag of an explanatory variable in a panel spatial model?

I am doing a spatial durbin model with spml function (splm package), I have included as regressors a polynom (grade 2) and obviosly I need to include its spatial lag too. Unfortunately the function slag and lag.listw don't work with a poly…
Silvia
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Issues predicting with `nlme::gls`quadratic model fitted with `poly(..., 2)`

I have fitted a quadratic model with a variance structure that allows different variance levels per level of a factor, and I’m having trouble predicting on a new data set with 2 entries only. Here’s a reproducible…
Ceres
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Combine like terms in a polynomial equation

Not homework or anything, just personal interests on coding, learning it by myself currently. Found this question interesting online. Think if we have a list of number that's 1 2 2 4 3 6 4 2 5 4 that equals to 1x^2+2^4+3^6+4^2+5^4 How can I…
Kim James
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How to eliminate variables with p value > 0.7 before computing stepwise polynomial regression?

I am trying to run a stepwise regression using AIC (through step) with 1,400 variables, but my computer just freezes. It works if I include <300 variables (after 13 hrs of running). Is there a way to eliminate some of the variables (if p-value >.7)…
RegressionMan
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dplyr: Using poly function to generate polynomial coefficients

I want to append polynomial coefficient to data.frame as the example given below: df1 <- structure(list( Y = c(4, 4, 4, 4, 4, 8, 8, 8, 8, 8, 16, 16, 16, 16, 16, 32, 32, 32, 32, 32, 4, 4, 4, 4, 4, 8, 8, 8, 8, 8, 16, 16,…
MYaseen208
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Error using 'poly': 'degree' must be less than number of unique points while using 'effects' package

I am trying to use the effects package to create plots of effects in a linear mixed model. I specify the model fit1 <- lmer(Values ~ stimuli + timeperiod + scale(poly(distance.code,3,raw=FALSE))*habitat + wind.speed + (1|location.code), data=ex.df,…
parksnrec1
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Is there an inverse function for poly?

We can generate orthogonal polynomials in R with pp <- poly(cars$speed, 2) Is there a way to get the original values out of the result pp (inverse poly function)? In other words, what should the function f look like that returns the following…
Andri Signorell
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Use poly on dataframe column

I have a dataframe like so wood <- read_csv("/Users/name/Desktop/AR/Exercise data-20201109/woodstrength.csv") I select x and y x <- wood %>% select(Conc) y <- wood %>% select(Strength) The relationship can be modeled with a polynomial of degree 2…
Marcel Braasch
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lmer poly() function on interactions

My goal is to run a quadratic function using several IVs across time within subject. I have come across some code and am a little confused. Below is a reproducible example of what I am trying to run. Following the code will be my…
Severe_Dragomere
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How to plot lm slope modeled using poly()?

I need to plot the relationship between x and y where polynomials of x predict y. This is done using the poly() function in order to ensure polynomials are orthogonal. How do I plot this relationship considering linear, quadratic and cubic terms…
Eric M
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Separate F tests for different order terms in a polynomial with ANOVA in R?

I have a regression model with a polynomial term and I am using ANOVA to test for the significance of the terms. I have been asked to report the linear and quadratic terms separately for the polynomial term, but can't seem to do this in R using…
corn_bunting
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Why does R keep complaining that I'm giving the wrong type of matrix to my lm model when I'm not using matrices at all?

Specifically, I'm getting the error Error: variable 'poly(x, degree = i, raw = TRUE)' was fitted with type "nmatrix.2" but type "nmatrix.5" was supplied I was provided this starting code by my professor: f = function(x) { return(x**2) } #Set…
Mikayla Eckel Cifrese
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modifying lm coefficients - why is predict output shifted like it had modified intercept?

I have a lm model with mortality data depending on daily temperature. To estimate a possible adaptation to climate change, I would like to reduce the slope of the curve by 10%. Therefore, I modified the slope-coefficients of the lm model by…
Lyzzie777
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Why are polynomial multiple regression coefficients missing in poly?

I ran a polynomial multiple regression in R using poly, and in the output the coefficients of some combinations of the two variables (Unc and Window) are seem to be missing, and I cannot get my head around it. The input data can be downloaded from…
Istvan Gabor Hatvani
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