Mean of categorical variables from plyr package

Question

My categorical variable, risk, is divided into three groups: ADV, HHM, and POV.

I'm looking for the average of these three groups for four continuous variables: read.5, read.6, read.7, and read.8, which are reading scores from grades 5 to 8.

It's the,2:5 of my dataset and an old textbook example. I used the following code, which appears to be incorrect despite the fact that it is correct according to the textbook example:

ddply(.data = MPLS[,2:5],.variables =.(MPLS$risk), myrisk

na.rm = TRUE,.fun = mean)

Earlier today, I received an error message for a section of code that read:

mean(MPLS[,2:5], na.rm = TRUE) - mymeans

When I googled it, I discovered that the R software had changed, and I needed to find another to operate with.

Answer 1

df<-data.frame(risk= rep(c("ADV","HHM","POV"),10),
                read.5= rnorm(30,30),
                read.4= rnorm(30,30),
                read.3= rnorm(30,30),
                read.2= rnorm(30,30))
> head(df)
#  risk   read.5   read.4   read.3   read.2
#1  ADV 30.78281 30.00721 29.80906 29.25936
#2  HHM 29.76175 29.63864 29.39256 29.40070
#3  POV 29.00964 30.48258 29.20662 28.77509
#4  ADV 29.60631 30.35032 32.00376 30.70374
#5  HHM 31.38653 30.28896 29.48756 30.32430
#6  POV 30.33102 30.40897 29.55796 30.10585

library(dplyr)

df %>% group_by(risk) %>% summarise_all(mean)

# A tibble: 3 x 5
#  risk  read.5 read.4 read.3 read.2
#  <fct>  <dbl>  <dbl>  <dbl>  <dbl>
1 ADV     30.3   30.2   30.2   30.4
2 HHM     29.7   30.5   29.8   29.9
3 POV     29.3   30.2   29.9   30.2