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--- math121b:r [2020/04/20 08:36]
pzhou created
+++ math121b:r [2020/04/20 09:52] (current)
pzhou [Cheat Sheat]
@@ Line 5: / Line 5: @@
 reference: {{ :math121b:r-cheat-sheet-3.pdf | CheatSheat PDF}}
-assignment
-    a <- 10
-create a vector
-    a = c(2,3,8,0)
-| Function |What it Calculates	|
+=== variable manipulations ===
-| mean(x)  |Mean of the numbers in vector x. |
+| function | meaning |
-| median(x) |Median of the numbers in vector x |
+| c(1,3,4,5) | create a vector |
-| var(x) |Estimated variance of the population from which the numbers in vector x are sampled |
+| 2:5 | create a sequence (2,3,4,5)|
-| sd(x)	| standard deviation, square root of var(x) |
+| 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 |

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