Calculating upper and lower confidence intervals by group in dplyr summarise() - r

Question

I am trying to make a table that shows N (number of observations), percent frequency (of answers > 0), and the lower and upper confidence intervals for percent frequency, and I want to group this by type.
Example of data
dat <- data.frame(
"type" = c("B","B","A","B","A","A","B","A","A","B","A","A","A","B","B","B"),
"num" = c(3,0,0,9,6,0,4,1,1,5,6,1,3,0,0,0)
)
Expected output (with values filled in):
Type N Percent Lower 95% CI Upper 95% CI
A
B
Attempt
library(dplyr)
library(qwraps2)
table<-dat %>%
group_by(type) %>%
summarise(N=n(),
mean.ci = mean_ci(dat$num),
"Percent"=n_perc(num > 0))
This worked to get N and percent frequency, but returned an error: "Column must be length 1 (a summary value), not 3" when I added in mean_ci
The second code I tried, found here:
table2<-dat %>%
group_by(type) %>%
summarise(N.num=n(),
mean.num = mean(dat$num),
sd.num = sd(dat$num),
"Percent"=n_perc(num > 0)) %>%
mutate(se.num = sd.num / sqrt(N.num),
lower.ci = 100*(mean.num - qt(1 - (0.05 / 2), N.num - 1) * se.num),
upper.ci = 100*(mean.num + qt(1 - (0.05 / 2), N.num - 1) * se.num))
# A tibble: 2 x 8
# type N.num mean.num sd.num Percent se.num lower.ci upper.ci
# <fct> <int> <dbl> <dbl> <chr> <dbl> <dbl> <dbl>
#1 A 8 2.44 2.83 "6 (75.00\\%)" 1.00 7.35 480.
#2 B 8 2.44 2.83 "4 (50.00\\%)" 1.00 7.35 480.
This gave me an output, but the confidence intervals are not logical.

Answer 1

The output of mean_ci is a vector of length 3. This is maybe unexpected because the package has added a print method so that when you see this in the console it looks like a single character value and not a numeric length > 1 vector. But, you can see the underlying data structure by looking at str.
mean_ci(dat$num) %>% str
# 'qwraps2_mean_ci' Named num [1:3] 2.44 1.05 3.82
# - attr(*, "names")= chr [1:3] "mean" "lcl" "ucl"
# - attr(*, "alpha")= num 0.05
In summarize, each element of each column of the output needs to be length 1, so providing a length 3 object for summarize to put in a single "cell" (column element) results in an error. A workaround is to put the length 3 vector in a list, so that it is now a length 1 list. Then you can use unnest_wider to separate it into 3 columns (and therefore making the table "wider")
library(tidyverse)
dat %>%
group_by(type) %>%
summarise( N=n(),
mean.ci = list(mean_ci(num)),
"Percent"= n_perc(num > 0)) %>%
unnest_wider(mean.ci)
# # A tibble: 2 x 6
# type N mean lcl ucl Percent
# <fct> <int> <dbl> <dbl> <dbl> <chr>
# 1 A 8 2.25 0.523 3.98 "6 (75.00\\%)"
# 2 B 8 2.62 0.344 4.91 "4 (50.00\\%)"

Answer 2

IceCreamToucan’s answer is very good. I’m posting this answer to offer a
different way to present the information.
library(dplyr)
#>
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:stats':
#>
#> filter, lag
#> The following objects are masked from 'package:base':
#>
#> intersect, setdiff, setequal, union
library(qwraps2)
dat <- data.frame("type" = c("B","B","A","B","A","A","B","A","A","B","A","A","A","B","B","B"),
"num" = c(3,0,0,9,6,0,4,1,1,5,6,1,3,0,0,0))
When building the dplyr::summarize call you can use the qwraps2::frmtci
call to format the output of qwraps2::mean_ci into a character string of
length one.
I would also recommend using the data pronoun .data so you can be explicit
about the variables to summarize.
dat %>%
dplyr::group_by(type) %>%
dplyr::summarize(N = n(),
mean.ci = qwraps2::frmtci(qwraps2::mean_ci(.data$num)),
Percent = qwraps2::n_perc(.data$num > 0))
#> `summarise()` ungrouping output (override with `.groups` argument)
#> # A tibble: 2 x 4
#> type N mean.ci Percent
#> <chr> <int> <chr> <chr>
#> 1 A 8 2.25 (0.52, 3.98) "6 (75.00\\%)"
#> 2 B 8 2.62 (0.34, 4.91) "4 (50.00\\%)"
Created on 2020-09-15 by the reprex package (v0.3.0)
devtools::session_info()
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