Question

Lets have the following dataframe inside R:

df <- data.frame(sample=rnorm(1,0,1),params=I(list(list(mean=0,sd=1,dist="Normal"))))
df <- rbind(df,data.frame(sample=rgamma(1,5,5),params=I(list(list(shape=5,rate=5,dist="Gamma")))))
df <- rbind(df,data.frame(sample=rbinom(1,7,0.7),params=I(list(list(size=7,prob=0.7,dist="Binomial")))))
df <- rbind(df,data.frame(sample=rnorm(1,2,3),params=I(list(list(mean=2,sd=3,dist="Normal")))))
df <- rbind(df,data.frame(sample=rt(1,3),params=I(list(list(df=3,dist="Student-T")))))

The first column contains a random number of a probability distribution and the second column stores a list with its parameters and name.
The dataframe df looks like:

      sample       params
1 0.85102972 0, 1, Normal
2 0.67313218  5, 5, Gamma
3 3.00000000 7, 0.7, ....
4 0.08488487 2, 3, Normal
5 0.95025523 3, Student-T

Q1: How can I have the list of name distributions for all records? df$params$dist does not work. For a single record is easy, for example the third one: df$params[[3]]$dist

Q2: Is there any alternative way of storing data like this? something like a multi-dimensional dataframe? I do not want to add columns for each parameter because it will scatter the dataframe with missing values.

Answer 1

It’s probably more natural to store information like this in a pure list structure, than in a data frame:

distList <- list(normal = list(sample=rnorm(1,0,1),params=list(mean=0,sd=1,dist="Normal")),
                    gamma = list(sample=rgamma(1,5,5),params=list(shape=5,rate=5,dist="Gamma")),
                    binom = list(sample=rbinom(1,7,0.7),params=list(size=7,prob=0.7,dist="Binomial")),
                    normal2 = list(sample=rnorm(1,2,3),params=list(mean=2,sd=3,dist="Normal")),
                    tdist = list(sample=rt(1,3),params=list(df=3,dist="Student-T")))

And then if you want to extract just the distribution name from each, we can use sapply to loop over the list and extract just that piece:

sapply(distList,function(x) x[[2]]$dist)
     normal       gamma       binom     normal2       tdist 
   "Normal"     "Gamma"  "Binomial"    "Normal" "Student-T"