Convert part of a statistical function's output into a data.frame - r

Question

I was wondering if there might be a way to turn the following part of the OUTPUT of the res and res2 objects into a data.frame?
Note: answer below works with res but not res2.
A functional answer is appreciated as the data below is just toy.
library(metafor)
dat <- dat.konstantopoulos2011
res <- rma.mv(yi, vi, random = ~ 1 | district/school, data=dat)
#== OUTPUT (CAN WE TURN ONLY BELOW PART INTO A data.frame?):
#Variance Components:
# estim sqrt nlvls fixed factor
#sigma^2.1 0.0651 0.2551 11 no district
#sigma^2.2 0.0327 0.1809 56 no district/school
#Test for Heterogeneity:
#Q(df = 55) = 578.8640, p-val < .0001
# AND
res2 <- rma.mv(yi, vi, random = ~ factor(school) | district, data=dat)
#== OUTPUT (CAN WE TURN ONLY BELOW PART INTO A data.frame?):
#Variance Components:
#outer factor: district (nlvls = 11)
#inner factor: factor(school) (nlvls = 11)
# estim sqrt fixed
#tau^2 0.0978 0.3127 no
#rho 0.6653 no
#Test for Heterogeneity:
#Q(df = 55) = 578.8640, p-val < .0001

Answer 1

If there is no default/standard way to extract the data then you can manipulate the output using capture.output.
return_data <- function(res) {
tmp <- capture.output(res)
#data start from second line after "Variance Components:"
start <- which(tmp == "Variance Components:") + 2
index <- which(tmp == "")
#Data ends before the empty line after "Variance Components:"
end <- index[which.max(index > start)] - 1
data <- read.table(text = paste0(tmp[start:end], collapse = '\n'), header = T)
heterogeneity_index <- which(tmp == "Test for Heterogeneity:") + 1
list(data = data, heterogeneity = tmp[heterogeneity_index])
}
res <- rma.mv(yi, vi, random = ~ 1 | district/school, data=dat)
return_data(res)
#$data
# estim sqrt nlvls fixed factor
#sigma^2.1 0.0651 0.2551 11 no district
#sigma^2.2 0.0327 0.1809 56 no district/school
#$heterogeneity
#[1] "Q(df = 55) = 578.8640, p-val < .0001"

Answer 2

Would this suit your purposes? The 'Test for Heterogeneity' doesn't really fit in the dataframe, so I added it as a seperate column and it gets duplicated as a result. I'm not sure how else you could do it.
library(tidyverse)
#install.packages("metafor")
library(metafor)
#> Loading required package: Matrix
#>
#> Attaching package: 'Matrix'
#> The following objects are masked from 'package:tidyr':
#>
#> expand, pack, unpack
#>
#> Loading the 'metafor' package (version 3.0-2). For an
#> introduction to the package please type: help(metafor)
dat <- dat.konstantopoulos2011
res <- rma.mv(yi, vi, random = ~ 1 | district/school, data=dat)
res
#>
#> Multivariate Meta-Analysis Model (k = 56; method: REML)
#>
#> Variance Components:
#>
#> estim sqrt nlvls fixed factor
#> sigma^2.1 0.0651 0.2551 11 no district
#> sigma^2.2 0.0327 0.1809 56 no district/school
#>
#> Test for Heterogeneity:
#> Q(df = 55) = 578.8640, p-val < .0001
#>
#> Model Results:
#>
#> estimate se zval pval ci.lb ci.ub
#> 0.1847 0.0846 2.1845 0.0289 0.0190 0.3504 *
#>
#> ---
#> Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
vc <- cbind(estim = res$sigma2,
sqrt = res$sigma,
nlvls = res$s.nlevels,
fixed = ifelse(res$vc.fix$sigma2, "yes", "no"),
factor = res$s.names,
R = ifelse(res$Rfix, "yes", "no"),
Test_for_heterogeneity = paste0("Q(df = ", res$k - res$p, ") = ", metafor:::.fcf(res$QE, res$digits[["test"]]), ", p-val ", metafor:::.pval(res$QEp,
res$digits[["pval"]], showeq = TRUE, sep = " "))
)
rownames(vc) <- c("sigma^2.1", "sigma^2.2")
result <- as.data.frame(vc)
result
#> estim nlvls fixed factor R Test_for_heterogeneity
#> sigma^2.1 "0.0650619442753117" "11" "no" "district" "no" "Q(df = 55) = 578.8640, p-val < .0001"
#> sigma^2.2 "0.0327365170279351" "56" "no" "district/school" "no" "Q(df = 55) = 578.8640, p-val < .0001"
Created on 2021-10-06 by the reprex package (v2.0.1)