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# SD FOR MEAN !!!

help how can I solve this ? We are working with the mtcars dataset and need to find the number of cars that fall into 1 standard deviation from the mean of the mpg column. This means that we need to find the cars that have the mpg value in the range of mean(mpg)-sd(mpg) and mean(mpg)+sd(mpg).

26th Jan 2022, 6:22 PM
yasmine saoud
6 Antworten
+ 2
# note the , ! x is a dataframe, not a vector! x<- mtcars[mtcars\$mpg<a &mtcars\$mpg>b,] # a x is a dataframe, you need to determine the number of rows, not the length nrow(x)
26th Jan 2022, 6:49 PM
Lisa
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You calculate the values and then filter the mpg column by them
26th Jan 2022, 6:33 PM
Lisa
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a<-mean(mtcars\$mpg)+sd(mtcars\$mpg) b<-mean(mtcars\$mpg)-sd(mtcars\$mpg) x<- mtcars[mtcars\$mpg<a &mtcars\$mpg>b] length(x) why is this wrong please ?
26th Jan 2022, 6:41 PM
yasmine saoud
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thank you I get it
26th Jan 2022, 7:06 PM
yasmine saoud
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x <- (mtcars\$mpg) a<-mean(mtcars\$mpg)-sd(mtcars\$mpg) b<-mean(mtcars\$mpg)+sd(mtcars\$mpg) tar <- mtcars[mtcars\$mpg>a & mtcars\$mpg<b,] print(nrow(tar))
11th Feb 2022, 12:42 PM