How to read column with column name `0.3` in R?

Question

library(ltm)
library(mokken)
data("LSAT")
df_aisp<-aisp(LSAT,search='normal')
df_aisp<-as.data.frame(df_aisp)
#subset if df_aisp$0.3==1
subset(df_aisp,0.3==1)

Output of above R script is:

[1] 0.3
<0 rows> (or 0-length row.names)

Actually,df_aisp is:

       0.3
Item 1   1
Item 2   0
Item 3   1
Item 4   0
Item 5   0

Which means subset give me wrong result.
How to solve this problem?

Answer 1

We can use backquotes for column names (to evaluate it as it is) that are not in standard format. By standard format, names starting with numbers.

subset(df_aisp,`0.3`==1)

Also, we can specify the column name quoted as such [[ or [ for subsetting

df_aisp[df_aisp[,"0.3"] ==1, , drop = FALSE]

---

However, we can make the names standard by using make.names which will add a prefix X to the column name

names(df_aisp) <- make.names(names(df_aisp))
names(df_aisp)
#[1] "X0.3"

Then, we don't need the backquotes

 subset(df_aisp, X0.3 == 1)
 #       X0.3
 #Item 1    1
 #Item 3    1