Get the length of the list stored in a column of data.frame

Question

I'm storing lists of strings in a column of my data.frame and I want to get lengths of those lists.

> class(df['4', "generated"])
[1] "list"
> summary(df['4', "generated"])
  Length Class  Mode     
4 180    -none- character
> length(df['4', "generated"])
[1] 1

As shown above df["4", "generated"] is of "list" class, but instead of expected result of length(df['4', "generated"]) being 180 it shows 1.

How do I get real list length, please?

UPD: I create data frame from JSON like this:

data <- fromJSON("out.json")
matrix <- cbind(id=names(data), t(rbind(sapply(data, "c")))) 
df <- data.frame(matrix)

and data looks something like this:

{ "4": 
    { "generated:
        ["00A1CD093DB15425310C2BB57CB88BA460C87E5B26BAB3867D26870914E80603",
         "018BE455F4A178A33517E3586AF115C9DF7356895B9A7416AD8D20D660B0866D",
         "04C5893516CE5C3A6ADC907EC1484DE7542189E9AC7F138EE57DF088EF2F9D92",
     <cut>]
    } 
}

Answer 1

Try:

length(df['4', "generated"][[1]])

And if that works for every list in the "generated" column:

sapply(sapply(df[,"generated",drop=F],"[[",1),length)