finding duplicate entries with duplicate()

I'm working with a data set from a long-term where plants get re-measured every year. Occasionally a new record gets inserted for a plant that already occurs in the data. This can be identified with the duplicated() command.

I can get a list that tells me TRUE/FALSE which regarding which entries are duplciated.

duplicated(data$tag)


This is a long list, so I can screen that output just for what is true by nesting the duplicated() command within a which() command

which(duplicated(data$tag) == TRUE)

The unique() command can also be used for similar task

Locating missing values with is.na()

When getting data ready for analysis, a very handy function is "is.na." It prints out a list of "TRUE" and "FALSE" responses for the status of every entry in a vector or column.

I have data from an experiment where I know the plot number is missing for a few entries. I can quickly identify these like this:

First, use is.na on the plot column and store the results (a LONG list of 2000 entries) to an object "na_plot"

na_plot<-is.na(reboot1$plot)

Second, use the which() function to query the list for the entries where the answer to the question "is.na" is "TRUE"

which(na_plot == TRUE)

This gives me the index number of the entries that are NA.