====== Programming in R ======
Cheat Sheat and Examples

==== Cheat Sheat ====
reference: {{ :math121b:r-cheat-sheet-3.pdf | CheatSheat PDF}}


=== variable manipulations ===
| function | meaning | 
| c(1,3,4,5) | create a vector |
| 2:5 | create a sequence (2,3,4,5)|
| y[3] | say y is a vector, take the 3rd entry out of y | 
| seq(2,10, by=0.5) | create a sequence, start from 2, ending at 10, step size = 0.5 | 
| rep(1:3, times = 2) | repeat the sequence (1,2,3), 2 times, so get (1,2,3,1,2,3) | 
| rep(1:3, each = 2) | repeat the sequence (1,2,3), each entry 2 times, so get (1,1,2,2,3,3) | 

=== if .. else .. ===
<code>
if (i > 3)
{ 
  print(‘Yes’)
} else { 
  print(‘No’)
}
</code>

=== For loop ===
<code>
for (i in 1:4)
{ 
  j <- i + 10
  print(j) 
}
</code>

=== function ===
<code>
square <- function(x)
{
   squared <- x*x
   return(squared)
}
</code>


==== Sampling ====

|Distribution | sampling | density function | cumulative density function |
| Normal | rnorm | dnorm | pnorm |
| Poisson | rpois | dpois | ppois |