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Setting it to "),a("code",[t._v("TRUE")]),t._v(" means that each element of the set being drawn from may appear more than once in the final result.")]),t._v(" "),a("div",{staticClass:"language-r extra-class"},[a("pre",{pre:!0,attrs:{class:"language-r"}},[a("code",[t._v("set.seed"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5062")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\nsample"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("x "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" c"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"A"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"B"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"C"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"D"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("size "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("8")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("replace "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token boolean"}},[t._v("TRUE")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"D"')]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"C"')]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"D"')]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"B"')]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"A"')]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"A"')]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"A"')]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"A"')]),t._v("\n\n")])])]),a("h3",{attrs:{id:"changing-draw-probabilities"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#changing-draw-probabilities"}},[t._v("#")]),t._v(" Changing Draw Probabilities")]),t._v(" "),a("p",[t._v("By default, when you use "),a("code",[t._v("sample")]),t._v(', it assumes that the probability of picking each element is the same. Consider it as a basic "urn" problem. The code below is equivalent to drawing a colored marble out of an urn 20 times, writing down the color, and then putting the marble back in the urn. The urn contains one red, one blue, and one green marble, meaning that the probability of drawing each color is 1/3.')]),t._v(" "),a("div",{staticClass:"language-r extra-class"},[a("pre",{pre:!0,attrs:{class:"language-r"}},[a("code",[t._v("set.seed"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("6472")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\nsample"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("x "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" c"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"Red"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"Blue"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"Green"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("\n       size "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("20")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("\n       replace "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token boolean"}},[t._v("TRUE")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n\n")])])]),a("p",[t._v("Suppose that, instead, we wanted to perform the same task, but our urn contains 2 red marbles, 1 blue marble, and 1 green marble. One option would be to change the argument we send to "),a("code",[t._v("x")]),t._v(" to add an additional "),a("code",[t._v("Red")]),t._v(". However, a better choice is to use the "),a("code",[t._v("prob")]),t._v(" argument to "),a("code",[t._v("sample")]),t._v(".")]),t._v(" "),a("p",[t._v("The "),a("code",[t._v("prob")]),t._v(" argument accepts a vector with the probability of drawing each element. In our example above, the probability of drawing a red marble would be 1/2, while the probability of drawing a blue or a green marble would be 1/4.")]),t._v(" "),a("div",{staticClass:"language-r extra-class"},[a("pre",{pre:!0,attrs:{class:"language-r"}},[a("code",[t._v("set.seed"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("28432")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\nsample"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("x "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" c"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"Red"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"Blue"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"Green"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("\n       size "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("20")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("\n       replace "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token boolean"}},[t._v("TRUE")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("\n       prob "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" c"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("0.50")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("0.25")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("0.25")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n\n")])])]),a("p",[t._v("Counter-intuitively, the argument given to "),a("code",[t._v("prob")]),t._v(" does not need to sum to 1. R will always transform the given arguments into probabilities that total to 1. For instance, consider our above example of 2 Red, 1 Blue, and 1 Green. You can achieve the same results as our previous code using those numbers:")]),t._v(" "),a("div",{staticClass:"language-r extra-class"},[a("pre",{pre:!0,attrs:{class:"language-r"}},[a("code",[t._v("set.seed"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("28432")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\nfrac_prob_example "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<-")]),t._v(" sample"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("x "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" c"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"Red"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"Blue"')]),a("span",{pre:!0,attrs:{class:"token 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number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token boolean"}},[t._v("TRUE")]),t._v("\n\n")])])]),a("p",[t._v("The major restriction is that you cannot set all the probabilities to be zero, and none of them can be less than zero.")]),t._v(" "),a("p",[t._v("You can also utilize "),a("code",[t._v("prob")]),t._v(" when "),a("code",[t._v("replace")]),t._v(" is set to "),a("code",[t._v("FALSE")]),t._v(". In that situation, after each element is drawn, the proportions of the "),a("code",[t._v("prob")]),t._v(" values for the remaining elements give the probability for the next draw. In this situation, you must have enough non-zero probabilities to reach the "),a("code",[t._v("size")]),t._v(" of the sample you are drawing. For example:")]),t._v(" "),a("div",{staticClass:"language-r extra-class"},[a("pre",{pre:!0,attrs:{class:"language-r"}},[a("code",[t._v("set.seed"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("21741")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\nsample"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("x "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" c"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"Red"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"Blue"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"Green"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("\n       size "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("2")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("\n       replace "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token boolean"}},[t._v("FALSE")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("\n       prob "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" c"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("0.8")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("0.19")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("0.01")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n\n")])])]),a("p",[t._v("In this example, Red is drawn in the first draw (as the first element). There was an 80% chance of Red being drawn, a 19% chance of Blue being drawn, and a 1% chance of Green being drawn.")]),t._v(" "),a("p",[t._v("For the next draw, Red is no longer in the urn. The total of the probabilities among the remaining items is 20% (19% for Blue and 1% for Green). For that draw, there is a 95% chance the item will be Blue (19/20) and a 5% chance it will be Green (1/20).")]),t._v(" "),a("h2",{attrs:{id:"setting-the-seed"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#setting-the-seed"}},[t._v("#")]),t._v(" Setting the seed")]),t._v(" "),a("p",[t._v("The "),a("code",[t._v("set.seed")]),t._v(" function is used to set the random seed for all randomization functions. If you are using R to create a randomization that you want to be able to reproduce, you should use "),a("code",[t._v("set.seed")]),t._v(" first.")]),t._v(" "),a("div",{staticClass:"language-r extra-class"},[a("pre",{pre:!0,attrs:{class:"language-r"}},[a("code",[t._v("set.seed"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1643")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\nsamp1 "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<-")]),t._v(" sample"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("x "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("size "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("200")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("replace "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token boolean"}},[t._v("TRUE")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n\nset.seed"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1643")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\nsamp2 "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<-")]),t._v(" sample"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("x "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("size "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("200")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("replace "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token boolean"}},[t._v("TRUE")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" identical"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("x "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" samp1"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("y "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" samp2"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token boolean"}},[t._v("TRUE")]),t._v("\n\n")])])]),a("p",[t._v("Note that parallel processing requires special treatment of the random seed, described more elsewhere.")]),t._v(" "),a("h4",{attrs:{id:"remarks"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#remarks"}},[t._v("#")]),t._v(" Remarks")]),t._v(" "),a("p",[t._v("Users who are coming from other programming languages may be confused by the lack of a "),a("code",[t._v("rand")]),t._v(" function equivalent to what they may have experienced before. Basic random number generation is done using the "),a("code",[t._v("r*")]),t._v(" family of functions for each distribution (see the link above). Random numbers drawn uniformly from a range can be generated using "),a("code",[t._v("runif")]),t._v(', for "random uniform". Since this also looks suspiciously like "run if", it is often hard to figure out for new R users.')])])}),[],!1,null,null,null);s.default=n.exports}}]);