Get the longest list item

Question

Suppose you have a data.frame list like

dfs <- list(
  a = data.frame(x = c(1:4, 7:10), a = runif(8)),
  b = data.frame(x = 1:10, b = runif(10)),
  c = data.frame(x = 1:10, c = runif(10))
)

Now I would like to extract the longest data.frame or data.frames file in this list. How?

I am stuck at this point:

library(plyr)
lengths <- lapply(dfs, nrow)
longest <- max(lengths)

+4

vanao veneri Jan 12 '16 at 15:11

2 answers

cnt <- sapply(dfs, nrow)
dfs[cnt == max(cnt)]

Or, if you only need the first occurrence of the maximum length:

dfs[which.max(cnt)]

+4

mlegge Jan 12 '16 at 15:14

Deveaup · Accepted Answer · 2016-01-12T15:23:50+0000

There are two built-in functions in R that can solve your question in my opinion:

which.max: returns the index of the first element of your list, which is max
```
> which.max(lengths)
[1] 2
```
which function returns all indexes that are TRUE Here:
```
> which(lengths==longest)
[1] 2 3 
```

Then you can multiply your list by the desired item:

dfs[which(lengths==longest)]

will return b and c to your example.