cdf - 5 months ago 12

R Question

i have a question regarding my second function which is not producing what i wanted to

`#example for mt-cars`

selected_cyl_6 <- subset(mtcars, mtcars$cyl==6)

selected_cyl_4 <- subset(mtcars, mtcars$cyl==4)

count <- function(variable,group) {

sum(group[[deparse(substitute(variable))]]== 4)

}

#now i would like to create a matrix with the results like here below:

#example

u<-count(gear,selected_cyl_6)

v<-count(carb,selected_cyl_6)

w<-count(gear,selected_cyl_4)

x<-count(carb,selected_cyl_4)

matrix(c(u,v,w,x), byrow=TRUE, ncol=2, nrow=2)

this is a feasible option, however i would love to convert the lines above into a function because in my dataset there are a lot more variables and i would save a lot of time and code length. i tried it with the following code:

`variables_of_interest <- c("gear","carb")`

groups_of_interest <- c("selected_cyl_6","selected_cyl_4")

alteration_multiple <- function(variable_vector, group_vector){

m.results <- matrix(0, nrow = length(variable_vector), ncol = length(group_vector))

rownames(m.results) <- variable_vector

colnames(m.results) <- group_vector

for (t in 1:length(group_vector)) {

for (i in 1:length(variable_vector)) {

m.results[i,t] <- count(group_vector[t],variable_vector[i])

}

print(m.results)

}

}

alteration_multiple(variable_vector=variables_of_interest, group_vector=groups_of_interest)

any suggestions? thank you so much for your support!

Answer

If you're going to use quoted strings to refer to data and variables, we need to modify your two functions.

The main task is to redefine the `count`

function so that it can handle your proposed inputs. We can use `eval`

and `as.name`

to do this.

```
count2 <- function(variable,group) {
sum(eval(as.name(group))[[variable]]== 4)
}
```

```
alteration_multiple2 <- function(variable_vector, group_vector){
m.results <- matrix(0, nrow = length(variable_vector), ncol = length(group_vector))
rownames(m.results) <- variable_vector
colnames(m.results) <- group_vector
for (t in 1:length(group_vector)) {
for (i in 1:length(variable_vector)) {
m.results[i,t] <- count2(variable_vector[i], group_vector[t])
}
}
return(m.results)
}
```

```
variables_of_interest <- c("gear","carb")
groups_of_interest <- c("selected_cyl_6","selected_cyl_4")
alteration_multiple2(variable_vector=variables_of_interest, group_vector=groups_of_interest)
selected_cyl_6 selected_cyl_4
gear 4 8
carb 4 0
```

We can avoid a `for`

loop and execute our function using `matrix`

, `apply`

, and `expand.grid`

.

```
alteration_multiple3 <- function(variables, groups){
matrix(
apply(
expand.grid(variables, groups), 1,
function(x) count2(x[1],x[2])),
nrow = length(variables),
ncol = length(groups),
dimnames = list(variables, groups))
}
```