Getting mean and standard deviation from groups in a data.frame

Question

I have heart rate data in the form of a list with the four categories 1AS, 1CS, 1AI, 1CI each of variable size. I would like to output mean and standard deviations for each

Answer 1

Another solution using ave:

ave(DF$HR, DF$Group)

gives the mean and

ave(DF$HR, DF$Group, FUN=sd)

with DF being your data frame.

Answer 2

Assuming your data is in a data.frame called DF:

by(DF$HR,DF$Group,mean)

# DF$Group: 1AI
# [1] 276
# ------------------------------------------------------------------------------------------------------------------------------------------------------------- 
# DF$Group: 1AS
# [1] 246.7692
# ------------------------------------------------------------------------------------------------------------------------------------------------------------- 
# DF$Group: 1CI
# [1] 217.625
# ------------------------------------------------------------------------------------------------------------------------------------------------------------- 
# DF$Group: 1CS
# [1] 227.25

by(DF$HR,DF$Group,sd)

# DF$Group: 1AI
# [1] 30.93946
# ------------------------------------------------------------------------------------------------------------------------------------------------------------- 
# DF$Group: 1AS
# [1] 36.48551
# ------------------------------------------------------------------------------------------------------------------------------------------------------------- 
# DF$Group: 1CI
# [1] 23.25595
# ------------------------------------------------------------------------------------------------------------------------------------------------------------- 
# DF$Group: 1CS
# [1] 25.77236