Jonas Lindeløv Jonas Lindeløv - 3 months ago 13
R Question

Table of mean (SD)s



I have a relatively large dataset, and I want to print a table of means and standard deviations for combinations of factors. I would like to have them in a format like this:

A B
test1 2.0 (1.0) 5.0 (2.0)
test2 6.3 (3.1) 2.1 (0.7)


Is there an easy way to do this?

The closest I get is using the
tables::tabular
function (minimal example):

# Example data
df = data.frame(
group=c('A', 'A', 'A', 'B', 'B', 'B'),
value=c(1,2,3,6,8,9))

# Print table
library(tables)
tabular(value ~ group * (mean + sd), df)


... which outputs this:

group
A B
mean sd mean sd
value 2 1 7.667 1.52


But I haven't figured out a neat way to transform this format to the
mean (SD)
format above. Note: These examples are very minimal. I will have a larger hierarchy (currently 4 x (mean+sd) columns and 2 x 3 rows) but the fundamental problem is the same.

Answer
library(reshape2)

formatted.table <- dcast(df, 'value' ~ group, fun.aggregate = function(x) {
    return(sprintf('%0.1f (%0.1f)', mean(x), sd(x)))
})

# "value"         A         B
#   value 2.0 (1.0) 7.7 (1.5)

Similar to Chris's answer, but a little bit cleaner (and no "test" variable needed).

You can also do this type of aggregation with the dplyr package.

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