R data exploration

histograms for all numeric variables in data frame
https://www.r-bloggers.com/quick-plot-of-all-variables/

> dataset %>%
+ keep(is.numeric) %>%
+ gather() %>%
+ ggplot(aes(value)) +
+ facet_wrap(~key, scales = "free") +
+ geom_histogram()

Plotting in R
http://www.stat.wisc.edu/~larget/stat302/chap2.pdf


data frame column types
numeric
double
interger
logical
factor

messy data frames
http://www.win-vector.com/blog/2015/04/what-can-be-in-an-r-data-frame-column/
POSIXlt
Arbitrary lists
Matrices
Data frames