# no.at.risk: Function to compute the number of individuals at risk In survcomp: Performance Assessment and Comparison for Survival Analysis

## Description

Function to compute the number of individuals at risk at certain time points, as used in the Kaplan-Meier estimator for instance, depending on stratification.

## Usage

 `1` ```no.at.risk(formula.s, data.s, sub.s = "all", t.step, t.end) ```

## Arguments

 `formula.s` formula composed of a `Surv` object and a strata variable (i.e. stratification). `data.s` data frame composed of the variables used in the formula. `sub.s` vector of booleans specifying if only a subset of the data should be considered. `t.step` time step at which the number of individuals at risk is computed. `t.end` maximum time to be considered.

## Details

The original version of this function was kindly provided by Dr Christos Hatzis (January, 17th 2006).

## Value

number of individuals at risk at each time step specified in `t.step` up to `t.end`.

## Author(s)

Christos Hatzis, Benjamin Haibe-Kains

`survfit`, `km.coxph.plot`
 ```1 2 3 4 5 6 7 8 9``` ```set.seed(12345) stime <- rexp(100) cens <- runif(100,.5,2) sevent <- as.numeric(stime <= cens) stime <- pmin(stime, cens) strat <- sample(1:3, 100, replace=TRUE) dd <- data.frame("surv.time"=stime, "surv.event"=sevent, "strat"=strat) no.at.risk(formula.s=Surv(surv.time,surv.event) ~ strat, data.s=dd, sub.s="all", t.step=0.05, t.end=1) ```