Essentially what I want to do is only use the summary() function in r only on specific columns of my df.
Basically doing this (using the cars df as an example):
cars_summary <- summary(cars)
speed_summary <- cars_summary$speed
When I try to do this I get an error saying:
$ operator is invalid for atomic vectors
What does that mean and is there a way to do this without sapply()?
Thanks!
Up front, I think you can do just summary(cars$speed) to get what you want.
summary(cars$speed)
# Min. 1st Qu. Median Mean 3rd Qu. Max.
# 4.0 12.0 15.0 15.4 19.0 25.0
If you will want this for multiple columns, and speed is just one example, then try this:
cars_summary <- lapply(cars, summary)
cars_summary$speed
# Min. 1st Qu. Median Mean 3rd Qu. Max.
# 4.0 12.0 15.0 15.4 19.0 25.0
However, there are some other things going on.
The column names of the summary matrix are buffered/padded so that the names appear to be centered over the stats. This is purely aesthetic, but they do make it a little unpredictable (well, not-easy) to capture.
cars_summary <- summary(cars)
dimnames(cars_summary)
# [[1]]
# [1] "" "" "" "" "" ""
# [[2]]
# [1] " speed" " dist"
It's a matrix, so you cannot use $-indexing on it. One would instead need to use [,"speed"] or whatever.
cars_summary[," speed"]
#
# "Min. : 4.0 " "1st Qu.:12.0 " "Median :15.0 " "Mean :15.4 " "3rd Qu.:19.0 " "Max. :25.0 "
### or perhaps
colnames(cars_summary) <- names(cars)
cars_summary[,"speed"]
#
# "Min. : 4.0 " "1st Qu.:12.0 " "Median :15.0 " "Mean :15.4 " "3rd Qu.:19.0 " "Max. :25.0 "
Hrrmmm, it's a matrix, but it's a matrix of strings, as you can see above and here:
### back to the original cars_summary
str(cars_summary)
# 'table' chr [1:6, 1:2] "Min. : 4.0 " "1st Qu.:12.0 " "Median :15.0 " "Mean :15.4 " "3rd Qu.:19.0 " "Max. :25.0 " ...
# - attr(*, "dimnames")=List of 2
# ..$ : chr [1:6] "" "" "" "" ...
# ..$ : chr [1:2] " speed" " dist"
While one could certainly use some patterns or such to extract those numbers, there will be loss of precision/accuracy.