Error using predict.lm: operator is invalid for atomic vectors

Question

I'm trying to use the pred function with a list but it seems that I have a problem. When I compute it it is written:

Error : $ operator is invalid for atomic vectors

This is my code:

for (i in 1:30) {
a=i
print(a)   
df[,4][df[,1]==a] <- exp(predict.lm(summary_of_lm[[a]][1], newdata = df[df[,1]==a,])) }

I want to iterate a prediction for the regression I made over 30 years. Those are stocked in a list summary_of_lm that is: summary_year_1, summary_year_2 ... Those are the matrix that stocked the coefficient, std errors etc... What I don't understand is that I am not using the $ sign and I have this error.

> class(summary_of_lm)
[1] "list"
> class(summary_of_lm[[a]])
[1] "matrix"

Detail: I also already declared all the parameters with the same variable name for df and summary_year_i in order to make the pred works.

Answer 1

I am not sure if you are looking for this where a below is the list of all datasets(for your example it can be like for year 1995,1996 and so on)

a<-split(mydata,mydata$cyl)
myprediction<-Map(function(x)predict(lm(mpg~cyl,data=x)),a)
> myprediction
$`4`
    Datsun 710      Merc 240D       Merc 230       Fiat 128    Honda Civic Toyota Corolla  Toyota Corona 
      26.66364       26.66364       26.66364       26.66364       26.66364       26.66364       26.66364 
     Fiat X1-9  Porsche 914-2   Lotus Europa     Volvo 142E 
      26.66364       26.66364       26.66364       26.66364 

$`6`
     Mazda RX4  Mazda RX4 Wag Hornet 4 Drive        Valiant       Merc 280      Merc 280C   Ferrari Dino 
      19.74286       19.74286       19.74286       19.74286       19.74286       19.74286       19.74286