File:KMcurve.png

library(survival)
plot(leukemia.surv <- survfit(Surv(time, status) ~ x, data = aml[7:17,] ) , lty=2:3)
# lty=2 is dashed, 3=dotted.
legend(100, .9, c("Maintenance", "No Maintenance"), lty = 2:3) 
title("Kaplan-Meier Curves\nfor AML Maintenance Study")

library(dplyr)
leukemia.surv
#Call: survfit(formula = Surv(time, status) ~ x, data = aml[7:17, ])
#
#                n events median 0.95LCL 0.95UCL
#x=Maintained    5      3     48      34      NA
#x=Nonmaintained 6      5      8       5      NA

# Note the median column does not mean we take the median from a subset of data
# The median and its confidence interval are defined by drawing a horizontal line 
# at 0.5 on the plot of the survival curve and its confidence bands.
# https://www.rdocumentation.org/packages/survival/versions/3.1-12/topics/print.survfit

aml[7:17, ] %>% group_by(x) %>% summarise(median=median(time))
# A tibble: 2 x 2
  x             median
  <fct>          <dbl>
1 Maintained        45
2 Nonmaintained      8

aml[7:17, ] %>% filter(status==1) %>% group_by(x) %>% summarise(median=median(time))
# A tibble: 2 x 2
  x             median
  <fct>          <dbl>
1 Maintained        34
2 Nonmaintained      8