Using mtabuate
from the qdapTools package that I maintain:
library(qdapTools)
mtabulate(strsplit(as.character(dat[[1]]), "https://stackoverflow.com/"))
## V1 ca cbr_LBL cni_at.p3x.4 eq2_off eq2_on fe.gr hi.on hi.ov put sent_1 sent_1fe.gr
## 1 1 1 0 0 1 1 1 0 0 1 1 0
## 2 1 1 0 0 1 1 1 1 1 1 1 0
## 3 1 1 0 0 1 1 0 1 1 1 0 1
## 4 1 1 0 1 1 1 1 0 0 1 1 0
## 5 1 1 1 0 1 1 1 0 0 1 1 0