R dataframe with nested vector - r

Question

Background
In R this works:
> df <- data.frame(a=numeric(), b=numeric())
> rbind(df, list(a=1, b=2))
a b
1 1 2
But if I want the list to have a vector, rbind fails:
> df <- data.frame(a=numeric(), b=vector(mode="numeric"))
> rbind(df, list(a=1, b=c(2,3)))
Error in rbind(deparse.level, ...) :
invalid list argument: all variables should have the same length
And if I try to specify the vector length, declaring the dataframe fails:
> df <- data.frame(a=numeric(), b=vector(mode="numeric", length=2))
Error in data.frame(a = numeric(), b = vector(mode = "numeric", length = 2)) :
arguments imply differing number of rows: 0, 2
Finally, if I eschew declaring the dataframe and try rbind two lists directly, it looks like everything is working, but the datatypes are all wrong, and none of the columns appear to exist.
> l1 <- list(a=1, b=c(2,3))
> l2 <- list(a=10, b=c(20,30))
> obj <- rbind(l1, l2)
> obj
a b
l1 1 Numeric,2
l2 10 Numeric,2
> typeof(obj)
[1] "list"
> obj$a
NULL
> obj$b
NULL
> names(obj)
NULL
My setup
I have a embedded device that gathers data every 50ms and spits out a packet of data. In my script, I'm parsing a waveform that represents the states of that process (process previous frame and transmit, gather new data, dead time where nothing happens) with a state machine. For each packet I'm calculating the duration of the process period, the gathering data period which is subdivided into 8 or 16 acquisition cycles, where I calculate the time of each acquisition cycle, and the remaining dead time.
My list basically looks like `list(process=#, cycles=c(#,#,#,#), deadtime=#). Different packet types have different cycle lengths, so I pass that in as a parameter and I want the script to work on any packet time.
My question
Is there a way to declare a dataframe that does what I want, or am I using R in a fundamentally wrong way and I should break each cycle into it's own list element? I was hoping to avoid the latter as it will make treating the cycles as a group more difficult.
I will note that I've just started learning R so I'm probably doing some odd things with it.
Expected output
If I were to process 4 packets worth of signal with 3 acq. cycles each, this would be my ideal output:
df <- data.frame(processTime=numeric(), cyles=???, deadtime=numeric())
df <- rbind(df, list(processTime=0.05, cycles=c(0.08, 0.10, 0.07), deadtime=0.38)
etc...
processTime cycles deadtime
1 0.05 0.08 0.10 0.07 0.38
2 0.06 0.07 0.11 0.09 0.36
3 0.07 0.28 0.11 0.00 0.00
4 0.06 0.08 0.08 0.09 0.41

Answer 1

I'll take a different stab. Dealing with just your first 2 records.
processTime<-c(.05,.06)
cycles<-list(list(.08,.10,.07), list(.07,.09,.38))
deadtime<-c(.38,.36)
For cycles, we created a list element with a list that contains 3 elements in it. So cycles[[1]][1] would refer to .08, and cycles[[1]][2] would refer second element of the first list and cycles[[2]][3] would refer to the 3rd item in the second list.
If we use cbind to bind these we get the following:
test<-as.data.frame(cbind(processTime,cycles,deadtime))
test
processTime cycles deadtime
1 0.05 0.08, 0.10, 0.07 0.38
2 0.06 0.07, 0.09, 0.38 0.36
test$cycles[[1]] will return first list
test$cycles[[1]]
[[1]]
[[1]][[1]]
[1] 0.08
[[1]][[2]]
[1] 0.1
[[1]][[3]]
[1] 0.07
Whereas the 3rd element of the second list can be called with:
test$cycles[[2]][3]
[[1]]
[1] 0.38
You can also unlist later for calculations:
unlist(test$cycles[[2]])
[1] 0.07 0.09 0.38
To do this iteratively as you requested.
test<-data.frame()
processTime<-c(.05)
cycles<-list(list(.08,.10,.07))
deadtime<-c(.38)
test<-as.data.frame(cbind(processTime,cycles,deadtime))
test
processTime cycles deadtime
1 0.05 0.08, 0.10, 0.07 0.38
processTime<-c(.06)
cycles<-list(list(.07,.09,.38))
deadtime<-c(.36)
test<- rbind(test,as.data.frame(cbind(processTime,cycles,deadtime)))
test
processTime cycles deadtime
1 0.05 0.08, 0.10, 0.07 0.38
2 0.06 0.07, 0.09, 0.38 0.36