tapply with non numeric values

Question

I'm in a class learning R right now, and I'm stuck on a problem.

We set up the following data frame:

Column1=c(rep("control",300),rep("ConditionB",300),rep("ConditionC",300))
Column2=(900,mean=100,sd=10)
data=data.frame(Column1,Column2)

It runs fine, but then he asked us the following request:

"Use tapply to find the means of "control", "ConditionB", and "ConditionC"".

I have tried ten different ways of putting it, and I just come out with errors. Can anyone help me with this?

I guess you missed a `rnorm` in your second line. Just try `tapply(data$Column2,data$Column1,mean)` — nicola, Dec 20 '14 at 22:11
possible duplicate of [Getting the mean value for every Id in a data frame](http://stackoverflow.com/questions/3797083/getting-the-mean-value-for-every-id-in-a-data-frame) — Henrik, Dec 20 '14 at 22:18

Steven Beaupré · Accepted Answer · 2014-12-20T22:25:39.090

1

As mentioned in the comments, you missed an rnorm(). You can also use the vector c("control","ConditionB","ConditionC") and times = 300 instead of repeating rep() 3 times.

Column1=rep(c("control","ConditionB","ConditionC"), times = 300)
Column2=rnorm(900,mean=100,sd=10)
data=data.frame(Column1,Column2)
tapply(data$Column2,data$Column1,mean)

edited Dec 20 '14 at 22:25

answered Dec 20 '14 at 22:15

Steven Beaupré

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@MaryHeske No need to thank me. Just mark the answer as "Accepted" if it fixes your problem. – Steven Beaupré Dec 20 '14 at 23:03

score 1 · Answer 2 · answered Dec 21 '14 at 01:29

1

In addition to use tapply, try hadley's package dplyr:

data %>% group_by(Column1) %>% summarise(mean(Column2))

answered Dec 21 '14 at 01:29

yang

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tapply with non numeric values

2 Answers2