I am trying to understand what is causing this bug in my R code and I feel like R is gaslighting me.

The sample() function seems to change depending on how I assign it?

Anyways, here is the MRE:

#Sampling Bug MRE
rm(list = ls())
library(tidyverse)
ages=c(paste0("CHILD",seq(1,10),"AGE"))
set.seed(26)
df=c()
for(i in 1:10){
  x=round(runif(1:100,min=1,max=20),0)
  df = as.data.frame(cbind(df,x))
}
names(df)=ages

set.seed(26)
df$`Sampled Child`=0
test_vector=c()
for(i in 1:nrow(df)){
  childs_age = unlist(c(as.numeric(df[i,ages])))
  slice=which(childs_age<=17)
  if(length(slice)>=1){
    df$`Sampled Child`[i]=sample(x=slice,size=1,replace = F)
    test_vector=append(test_vector,sample(x=slice,size=1,replace = F))
  }
  else{
    df$`Sampled Child`[i]="Ineligibile"
    test_vector=append(test_vector,"Ineligibile")
  }
}
df$test=test_vector
sum(df$`Sampled Child`==df$test)

I just need someone to explain why assigning the value with df$Sampled Child[i] is assigning a different number than just appending it to a vector?

TIA!

I am trying to sample a child who is less than 17 years old only. Once I know which children are less than 17, I pick one at randomly. If there are no children less than 17, they are ineligible.