R Under development (unstable) (2023-08-12 r84939 ucrt) -- "Unsuffered Consequences"
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> library(survival)
> options(na.action=na.exclude) # preserve missings
> options(contrasts=c('contr.treatment', 'contr.poly')) #ensure constrast type
> 
> #
> # Simple tests of concordance
> #
> aeq <- function(x,y, ...) all.equal(as.vector(x), as.vector(y), ...)
> 
> grank <- function(x, time, grp, wt) 
+     unlist(tapply(x, grp, rank))
> grank2 <- function(x, time, grp, wt) {  #for case weights
+     if (length(wt)==0) wt <- rep(1, length(x))
+     z <- double(length(x))
+     for (i in unique(grp)) {
+         indx <- which(grp==i)
+         temp <- tapply(wt[indx], x[indx], sum)
+         temp <- temp/2  + c(0, cumsum(temp)[-length(temp)])
+         z[indx] <- temp[match(x[indx], names(temp))]
+     }
+     z
+ }
> 
> # Concordance by brute force.  O(n^2) algorithm, but ok for n<500 or so
> allpair <- function(x, time, status, wt, all=FALSE) {
+     if (missing(wt)) wt <- rep(1, length(x))
+     count <- sapply(which(status==1), function(i) {
+         atrisk <- (time > time[i]) | (time==time[i] & status==0)
+         temp <- tapply(wt[atrisk], factor(sign(x[i] -x[atrisk]), c(1, -1, 0)),
+                        sum)
+         wt[i]* c(ifelse(is.na(temp), 0, temp),
+                  (sum(wt[time==time[i] & status==1]) - wt[i])/2) 
+     })
+     rownames(count) <- c("concordant", "discordant", "tied.x", "tied.y")
+     if (all) {
+         colnames(count) <- time[status==1]
+         t(count)
+     }
+     else rowSums(count)
+ }
> 
> 
> # The std of C = std(numerator)/(number of comparable pairs)
> # The information matrix of a Cox model is = to the var(C-D)
> cfun <- function(fit) fit$cvar * sum(fit$count[1:3])^2
>                 
> tdata <- aml[aml$x=='Maintained', c("time", "status")]
> tdata$x <- c(1,6,2,7,3,7,3,8,4,4,5)
> tdata$wt <- c(1,2,3,2,1,2,3,4,3,2,1)
> fit <- concordance(Surv(time, status) ~x, tdata)
> 
> aeq(fit$count[1:4], c(24,14,2,0))
[1] TRUE
> cfit <- coxph(Surv(time, status) ~ tt(x), tdata, tt=grank, method='breslow',
+               iter=0, x=T)
> cdt <- coxph.detail(cfit)
> aeq(sum(cdt$imat), cfun(fit))
[1] TRUE
> aeq(sum(2*cdt$score), diff(fit$count[1:2]))
[1] TRUE
> aeq(with(tdata, allpair(x, time, status)), c(14,24,2,0))
[1] TRUE
> 
> # Lots of ties
> tempy <- Surv(c(1,2,2,2,3,4,4,4,5,2), c(1,0,1,0,1,0,1,1,0,1))
> tempx <- c(5,5,4,4,3,3,7,6,5,4)
> fit2 <- concordance(tempy ~ tempx)
> addxy <- function(x) c(x[1:3], sum(x[4:5]))
> aeq(addxy(fit2$count), allpair(tempx, tempy[,1], tempy[,2]))
[1] TRUE
> cfit2 <-  coxph(tempy ~ tt(tempx), tt=grank, method='breslow', iter=0)
> aeq(cfit2$var, 1/cfun(fit2))
[1] TRUE
> 
> # Direct call
> fit2b <- concordancefit(tempy, tempx)
> fit2c <- concordancefit(tempy, tempx, std.err=FALSE)
> all.equal(fit2[1:5], fit2b)
[1] TRUE
> all.equal(fit2b[1:3], fit2c)
[1] TRUE
> 
> # Bigger data
> fit3 <- concordance(Surv(time, status) ~ age, lung, reverse=TRUE)
> aeq(addxy(fit3$count), allpair(lung$age, lung$time, lung$status-1))
[1] TRUE
> cfit3 <- coxph(Surv(time, status) ~ tt(age), lung, 
+                iter=0, method='breslow', tt=grank, x=T)
> cdt <- coxph.detail(cfit3)
> aeq(sum(cdt$imat), cfun(fit3)) 
[1] TRUE
> aeq(2*sum(cdt$score), diff(fit3$count[2:1]))
[1] TRUE
> 
> 
> # More ties
> fit4 <- concordance(Surv(time, status) ~ ph.ecog, lung, reverse=TRUE)
> aeq(addxy(fit4$count), allpair(lung$ph.ecog, lung$time, lung$status-1))
[1] TRUE
> aeq(fit4$count[1:5], c(8392, 4258, 7137, 21, 7))
[1] TRUE
> cfit4 <- coxph(Surv(time, status) ~ tt(ph.ecog), lung, 
+                iter=0, method='breslow', tt=grank)
> aeq(1/cfit4$var, cfun(fit4))
[1] TRUE
> 
> # Case weights
> fit5 <- concordance(Surv(time, status) ~ x, tdata, weight=wt, reverse=TRUE)
> fit6 <- concordance(Surv(time, status) ~x, tdata[rep(1:11,tdata$wt),])
> aeq(addxy(fit5$count), with(tdata, allpair(x, time, status, wt)))
[1] TRUE
> aeq(fit5$count[1:4], c(70, 91, 7, 0))  # checked by hand
[1] TRUE
> aeq(fit5$count[1:3], fit6$count[c(2,1,3)])  #spurious "tied on time" values, ignore
[1] TRUE
> aeq(fit5$std, fit6$std)
[1] TRUE
> cfit5 <- coxph(Surv(time, status) ~ tt(x), tdata, weight=wt, 
+                iter=0, method='breslow', tt=grank2)
> cfit6 <- coxph(Surv(time, status) ~ tt(x), tdata[rep(1:11,tdata$wt),], 
+                iter=0, method='breslow', tt=grank)
> aeq(1/cfit6$var, cfun(fit6))
[1] TRUE
> aeq(cfit5$var, cfit6$var)
[1] TRUE
> 
> # Start, stop simplest cases
> fit7 <- concordance(Surv(rep(0,11), time, status) ~ x, tdata)
> aeq(fit7$count, fit$count)
[1] TRUE
> aeq(fit7$std.err, fit$std.err)
[1] TRUE
> fit7 <- concordance(Surv(rep(0,11), time, status) ~ x, tdata, weight=wt)
> aeq(fit5$count, fit7$count[c(2,1,3:5)])  #one reversed, one not
[1] TRUE
> 
> # Multiple intervals for some, but same risk sets as tdata
> tdata2 <- data.frame(time1=c(0,3, 5,  6,7,   0,  4,17,  7,  0,16,  2,  0, 
+                              0,9, 5),
+                      time2=c(3,9, 13, 7,13, 18, 17,23, 28, 16,31, 34, 45, 
+                              9,48, 60),
+                      status=c(0,1, 1, 0,0,  1,  0,1, 0, 0,1, 1, 0, 0,1, 0),
+                      x = c(1,1, 6, 2,2, 7, 3,3, 7, 3,3, 8, 4, 4,4, 5),
+                      wt= c(1,1, 2, 3,3, 2, 1,1, 2, 3,3, 4, 3, 2,2, 1))
> fit8 <- concordance(Surv(time1, time2, status) ~x, tdata2, weight=wt,
+                     reverse=TRUE)
> aeq(fit5$count, fit8$count)
[1] TRUE
> aeq(fit5$std.err, fit8$std.err)
[1] TRUE
> cfit8 <- coxph(Surv(time1, time2, status) ~ tt(x), tdata2, weight=wt, 
+                iter=0, method='breslow', tt=grank2)
> aeq(1/cfit8$var, cfun(fit8))
[1] TRUE
> 
> # Stratified
> tdata3 <- data.frame(time1=c(tdata2$time1, rep(0, nrow(lung))),
+                      time2=c(tdata2$time2, lung$time),
+                      status = c(tdata2$status, lung$status -1),
+                      x = c(tdata2$x, lung$ph.ecog),
+                      wt= c(tdata2$wt, rep(1, nrow(lung))),
+                      grp=rep(1:2, c(nrow(tdata2), nrow(lung))))
> fit9 <- concordance(Surv(time1, time2, status) ~x + strata(grp),
+                         data=tdata3, weight=wt, reverse=TRUE)
> aeq(fit9$count[1,], fit5$count)
[1] TRUE
> aeq(fit9$count[2,], fit4$count)
[1] TRUE
> 
> proc.time()
   user  system elapsed 
   1.57    0.17    1.75