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# Start coding here...df
df <- mtcars
str(df)
df2 <-df[df$cyl == 4,]
mean(df2$hp)
tapply(df$hp, df$cyl, mean)
result <- aggregate(df$hp, list(df$cyl), FUN=mean)
typeof(result)
df[grepl("6|4", df$cyl),]
df[df$cyl == 4 | df$cyl == 6, ]
library(plyr)
library(plyr)
#df <- data.frame(cyl = c(4, 6, 8), gear = c(3, 4, 5), mpg = c(22, 18, 15))
smr <- ddply(df, .(cyl, gear), summarise, mpg2 = sum(mpg))
smr
str(smr)