Filtering data in a dataframe based on criteria

Question

I am new to R and can\'t get to grips with this concept. Suppose I have a table loaded called \"places\" with 3 say columns - city, population and average summer temperature

Answer 1

You are looking for subset

if your data is called mydata

newdata <- subset(mydata, city < 1e6)

Or you could use [, which is programatically safer

newdata <- mydata[mydata$city < 1e6]

For more than one condition use & or | where approriate

You could also use the sqldf package to use sql

library(sqldf)

newdata <-  sqldf('select * from mydata where city > 1e6')

Or you could use data.table which makes the syntax easier for [ (as well as being memory efficient)

library(data.table)

mydatatable <- data.table(mydata)
newdata <- mydatatable[city > 1e6]