# [R] Lapply to create sub categories based on categorical data

arun smartpink111 at yahoo.com
Sun Feb 2 23:40:17 CET 2014

```Hi,
Try:
x <- c(rep("A",0.1*10000),rep("B",0.2*10000),rep("C",0.65*10000),rep("D",0.05*10000))
set.seed(24)
categorical_data <- sample(x,10000)
set.seed(49)
p_val <- runif(10000,0,1)

combi <- data.frame(V1=categorical_data,V2=p_val)
variables <- unique(combi\$V1)
res <- lapply(levels(variables),function(x){ combi\$NEWVAR<-(combi\$V1==x)*1; combi})

A.K.

I was wondering if you kind folks could answer a question I have. In the sample data I've provided below, in column 1 I have a categorical
variable labeled A,B,C and D, and in column 2 simulated p-values.

x <- c(rep("A",0.1*10000),rep("B",0.2*10000),rep("C",0.65*10000),rep("D",0.05*10000))
categorical_data=as.matrix(sample(x,10000))
p_val=as.matrix(runif(10000,0,1))
combi=as.data.frame(cbind(categorical_data,p_val))

This is simulated data, but my example comes out as

V1                V2
1  A 0.484525170875713
2  C  0.48046557046473
3  C 0.228440979029983
4  B 0.216991128632799
5  C 0.521497668232769
6  D 0.358560319757089

I want to now take one of the categorical variables, let's say
"C", and create another variable (coded as 1 if it's C or 0 if it
isn't).

combi\$NEWVAR[combi\$V1=="C"] <-1
combi\$NEWVAR[combi\$V1!="C" <-0

V1                V2 NEWVAR
1  A 0.484525170875713 0
2  C  0.48046557046473 1
3  C 0.228440979029983 1
4  B 0.216991128632799 0
5  C 0.521497668232769 1
6  D 0.358560319757089 0

I'd like to do this for each of the variables in V1, creating a new table each time, by looping over using lapply:

variables=unique(combi\$V1)

loopeddata=lapply(variables,function(x){
combi\$NEWVAR[combi\$V1==x] <-1
combi\$NEWVAR[combi\$V1!=x]<-0
}
)

My output however looks like this:

[]
 0

[]
 0

[]
 0

[]
 0

My desired output would be like the table in the second block of
code, but when looping over the third column would be A=1, while
B,C,D=0. Then B=1, A,C,D=0 etc, for each table created.

Any help would me very much appreciated

```