分割数据框并计算R中数据子集的平均值

Question

I have this data frame in R:

steps   day         month  
4758    Tuesday     December
9822    Wednesday   December
10773   Thursday    December

I want to iterate over the data frame and apply a function to the steps column based on the value in the month column. I'm trying to work out the average number of steps per weekday for each month.

I want to output to a new data frame like so where the week days repeat but I only have the average values per day:

average.steps   day         month
4500            Tuesday     December
9000            Wednesday   December
1000            Thursday    December

I can work out how to work out the averages for the data frame as a whole, but want to use a for loop to apply it just for step values from the same month.

avgsteps <- ddply(DATA, "day", summarise, msteps = mean(steps))

My basic idea for the for function was:

f <- function(m in month) {ddply(DATA, "day", summarise, msteps = mean(steps))}

But it won't process it and throws the error:

Error: unexpected 'in' in "f <- function(m in"

Any help would be greatly appreciated!

EDIT:

SO I've tried @agstudy's suggested fix (below) and it gets the right data structure (single value for each weekday for each month), but the value assigned to each day is identical. I'm a bit confused what could be going wrong.

steps.month.day.avg <- ddply(steps.month.day, .(fitbit.day,fitbit.month), summarise, msteps = mean(steps))

Answer 1

无需在此处循环，您只需更改变量即可分割数据帧，

 ddply(DATA, .(day,month), summarise, msteps = mean(steps))