**Burns Statistics » R language**, and kindly contributed to R-bloggers)

Towards the basic R mindset.

## Previously

The post “A first step towards R from spreadsheets” provides an introduction to switching from spreadsheets to R. It also includes a list of additional posts (like this one) on the transition.

## Add two columns

Figure 1 shows some numbers in two columns and the start of adding those two columns to each other in a third column.

Figure 1: Adding two columns in a spreadsheet.

The next step is to fill the addition formula down the column.

It is not so different to do the same thing in R. First create two objects that are equivalent to the two columns in the spreadsheet:

A <- c(32.5, -3.8, 15.9, 22.5) B <- c(48.1, 19.4, 46.8, 14.7)

In those commands you used the `c`

function which **c**ombines objects. You have created two *vectors*. The rules for a vector are:

- it can be any length (up to a very large value)
- all the elements are of the same type — all numbers, all character strings or all logicals
- the order matters (just like it matters which row a number is in within a spreadsheet)

To summarize: they’re in little boxes and they all look just the same.

You have two R vectors holding your numbers. Now just add them together (and assign that value into a third name):

C <- A + B

This addition is precisely what is done in the spreadsheet: the first value in C is the first value in A plus the first value in B, the second value in C is the second value in A plus the second value in B, and so on.

See the values in an object by typing its name:

> C [1] 80.6 15.6 62.7 37.2

The “`> `

” is the R prompt, you type only what is after that: ‘`C`

‘ (and the return or enter key).

Also note that R is case-sensitive – `C`

and `c`

are different things:

> c function (..., recursive = FALSE) .Primitive("c")

(Don’t try to make sense of what this means other than that `c`

is a function.)

## Multiply by a constant

One way of multiplying a column by a constant is to multiply the values in the column by the value in a single cell. This is illustrated in Figure 2.

Figure 2: Multiply a column times the value in a single cell, shown before filling down column E.

Another way of doing the same thing is to fill the value in D1 down column D and then multiply the two columns.

Do this operation in R with:

> C * 33 [1] 2659.8 514.8 2069.1 1227.6

In this command you didn’t create a new object to hold the answer.

You can think of R as doing either of the spreadsheet methods, but the fill-down image might be slightly preferable.

## Recycling in R

The R recycling rule generalizes the idea of a single value expanding to the length of the vector. It is possible to do operations with vectors of different lengths where both have more than one element:

> 1:6 + c(100, 200) [1] 101 202 103 204 105 206

Figure 3 illustrates how R got to its answer.

Figure 3: Equivalent of the example of R’s recycling rule.

Column F shows how column G was created: use the ROW function and fill it down the column. That sequence of numbers was created in R with the ``:``

operator.

Note how the shorter vector is replicated to the length of the longer one. Each value is used in order, and when it reaches the end it goes back to the beginning again.

You are free to think this is weird. However, it is often useful.

## Functions

Table 1 translates between spreadsheet and R functions. The spreadsheets consulted were Excel, Works and OpenOffice. Note there is some variation between spreadsheets.

Table 1: Equivalent functions between spreadsheets and R.

spreadsheet | R | comment |

ABS | `abs` | |

ADDRESS | perhaps `assign` but there is probably a better way | |

AND | `all` | more literally would be the `&` and `&&` R operators |

AVERAGE | `mean` | danger: `mean` accepts only one data argument |

AVG | `mean` | this danger of `mean` is discussed in Circle 3 of The R Inferno |

AVERAGEIF | subscript before using `mean` | |

BESSELI | `besselI` | |

BESSELJ | `besselJ` | |

BESSELK | `besselK` | |

BESSELY | `besselY` | |

BETADIST | `pbeta` | |

BETAINV | `qbeta` | |

BINOMDIST | `pbinom` or `dbinom` | `pbinom` when cumulative, `dbinom` when not |

CEILING | `ceiling` | |

CELL | `str` is sort of the same idea | |

CHIDIST | `pchisq` | `CHIDIST(x, df)` is `pchisq(x, df, lower.tail=FALSE)` |

CHIINV | `qchisq` | `CHIINV(p, df)` is `qchisq(1-p, df)` |

CHISQDIST | `pchisq` or `dchisq` | `pchisq` when cumulative, `dchisq` when not |

CHISQINV | `qchisq` | |

CHITEST | `chisq.test` | |

CHOOSE | `switch` | |

CLEAN | `gsub` | |

COLS | ncol | (Works) |

COLUMNS | ncol | (Excel, OpenOffice) |

COLUMN | col | or probably more likely `:` or `seq` |

COMBIN | `choose` | |

CONCATENATE | `paste` | |

CONFIDENCE | CONFIDENCE(alpha, std, n) is `-qnorm(alpha/2) * std / sqrt(n)` | |

CORREL | `cor` | |

COUNT | `length` | |

COUNTIF | get length of a subscripted object | |

COVAR | `cov` | |

CRITBINOM | `qbinom` | `CRITBINOM(n, p, a)` is `qbinom(a, n, p)` |

DELTA | `all.equal` or `identical` | `all.equal` allows for slight differences, and note that it does not return a logical if there’s a pertinent difference — you can wrap it in `isTRUE` if you want |

DGET | use subscripting in R | |

ERF | see the example in `?"Normal"` | |

ERFC | see the example in `?"Normal"` | |

EXACT | `==` | EXACT is specific to text, `==` is not |

EXP | `exp` | |

EXPONDIST | `pexp` or `dexp` | `pexp` when cumulative, `dexp` when not |

FACT | `factorial` | |

FACTDOUBLE | `dfactorial` | `dfactorial` is in the `phangorn` package |

FDIST | `pf` | `FDIST(x, df1, df2)` is `pf(x, df1, df2, lower.tail=FALSE)` |

FIND | `regexpr` | |

FINV | `qf` | `FINV(p, df1, df2)` is `qf(1-p, df1, df2)` |

FISHER | `atanh` | |

FISHERINV | `tanh` | |

FIXED | `format` or `sprintf` or `formatC` | |

FLOOR | `floor` | |

FORECAST | `predict` on an `lm` object | |

FREQUENCY | you probably want to use `cut` and/or `table` | |

FTEST | `var.test` | |

GAMMADIST | `pgamma` or `dgamma` | `GAMMADIST(x, a, b, TRUE)` is `pgamma(x, a, scale=b)` `GAMMADIST(x, a, b, FALSE)` is `dgamma(x, a, scale=b)` |

GAMMAINV | `qgamma` | `GAMMAINV(p, a, b)` is `qgamma(p, a, scale=b)` |

GAMMALN | `lgamma` | |

GAUSS | GAUSS(x) is `pnorm(x) - 0.5` | |

GCD | `gcd` | `gcd` is in the `schoolmath` package (and others). For more than two numbers you can do: `Reduce(gcd, numVector)` |

GEOMEAN | `exp(mean(log(x)))` | |

GESTEP | `>=` | GESTEP(x, y) is `as.numeric(x >= y)` but R often coerces automatically if needed |

HARMEAN | `harmonic.mean` | `harmonic.mean` is in the `psych` package |

HLOOKUP | use subscripting in R | |

HYPGEOMDIST | `dhyper` | `HYPGEOMDIST(x, a, b, n)` is `dhyper(x, b, n-b, a)` |

IF | `if` or `ifelse` | see Circle 3.2 of The R Inferno on `if` versus `ifelse` |

IFERROR | `try` or `tryCatch` | |

INDEX | `[` | use subscripting in R |

INDIRECT | `get` | or possibly the eval-parse-text idiom, or (better) make changes that simplify the situation |

INT | `floor` | danger: not the same as `as.integer` for negative numbers |

INTERCEPT | (usually) the first element of `coef` of an `lm` object | |

ISLOGICAL | `is.logical` | |

ISNUMBER | `is.numeric` | |

ISTEXT | `is.character` | |

KURT | `kurtosis` | `kurtosis` is in the `moments` package |

LARGE | you can use subscripting after `sort` | |

LCM | `scm` | `scm` is in the `schoolmath` package. For more than two numbers you can do: `Reduce(scm, numVector)` |

LEFT | `substr` | |

LEN | `nchar` | (Excel, OpenOffice) |

LENGTH | `nchar` | (Works) |

LINEST | use `lm` | |

LN | log | danger: the default base in R for `log` is e |

LOG | log | danger: the default base in spreadsheets for `log` is 10 |

LOG10 | log10 | |

LOGINV | qlnorm | |

LOGNORMDIST | plnorm | |

LOWER | `tolower` | |

MATCH | `match` or `which` | `match` only does exact matches. Given that MATCH demands a sorted set of values for type 1 or -1, then MATCH(x, vec, 1) is `sum(x <= vec)` and MATCH(x, vec, -1) is `sum(x >= vec)` when `vec` is sorted as MATCH assumes. |

MAX | `max` or `pmax` | `max` returns one value, `pmax` returns a vector |

MDETERM | `det` | |

MEDIAN | median | |

MID | `substr` | |

MIN | `min` or `pmin` | `min` returns one value, `pmin` returns a vector |

MINVERSE | `solve` | |

MMULT | `%*%` | |

MOD | `%%` | |

MODE | the `table` function does the hard part. A crude approximation to MODE(x) is `as.numeric(names(which.max(table(x))))` | |

MUNIT | `diag` | `diag` is much more general |

N | `as.numeric` | the correspondence is for logicals, `as.numeric` is more general |

NEGBINOMDIST | `dnbinom` | |

NORMDIST, NORMSDIST | `pnorm` or `dnorm` | `pnorm` when cumulative is true, `dnorm` when false |

NORMINV, NORMSINV | `qnorm` | |

NOT | `!` | |

NOW | `date` or `Sys.time` | |

OR | `any` | the or operators in R are `|` and `||` |

PEARSON | `cor` | |

PERCENTILE | `quantile` | |

PERCENTRANK | similar to `ecdf` but the argument is removed from the distribution in PERCENTRANK | |

PERMUT | `function(n,k) {choose(n,k) * factorial(k)}` | |

PERMUTATIONA | PERMUTATIONA(n, k) is `n^k` | |

PHI | `dnorm` | |

POISSON | `ppois` or `dpois` | `ppois` if cumulative, `dpois` if not |

POWER | `^` | |

PROB | you can use the `Ecdf` function in the `Hmisc` package (the probabilities in the spreadsheet are the weights in `Ecdf` ), then you can get the difference of that on the two limits | |

PRODUCT | `prod` | |

PROPER | see example in `?toupper` | |

QUARTILE | use `quantile` | |

QUOTIENT | `%/%` | |

RAND | runif | see an introduction to random generation in R |

RANDBETWEEN | use `sample` | |

RANK | rank | RANK has the `"min"` tie.method and defaults to biggest first.`rank` only has smallest first. To get biggest first in R you can do: `length(x) + 1 - rank(x)` |

REPLACE | `sub` or `gsub` | |

REPT | use `rep` and `paste` or `paste0` | |

RIGHT | `substring` | you'll also need `nchar` to count the characters. Alternatively you can use `str_sub` in the `stringr` package with negative limits |

ROUND | `round` | note: `round` rounds exact halves to even (which avoids bias) |

ROUNDDOWN | `trunc` | `trunc` only goes to integers |

ROW | row | or probably more likely `:` or `seq` |

ROWS | `nrow` | |

RSQ | in `summary` of an `lm` object | |

SEARCH | `regexpr` | also see `grep` |

SIGN | `sign` | |

SKEW | skewness | `skewness` is in the `moments` package |

SLOPE | in `coef` of an `lm` object | |

SMALL | you can use subscripting after `sort` | |

SQRT | `sqrt` | |

STANDARDIZE | `scale` | |

STD | `sd` | (Works) |

STDEV | `sd` | (Excel, OpenOffice) |

STEYX | `predict` on an `lm` object | |

STRING | `format` or `sprintf` or `formatC` or `prettyNum` | (Works) |

SUBSTITUTE | `sub` or `gsub` | or possibly `paste` |

SUM | `sum` | `sum` is one of the few R functions that allow multiple data arguments |

SUMIF | subscript before using `sum` | |

SUMPRODUCT | `crossprod` | |

TDIST | `pt` | TDIST(abs(x), df, tails) is pt(-abs(x), df) * tails |

TEXT | `format` or `sprintf` or `formatC` or `prettyNum` | |

TINV | `TINV(x, df)` is `abs(qt(x/2, df))` | |

TODAY | `Sys.Date` | |

TRANSPOSE | `t` | |

TREND | `fitted` of an `lm` object | |

TRIM | `sub` | |

TRIMMEAN | `mean` | `TRIMMEAN(x, tr)` is `mean(x, trim=tr/2)` |

TRUNC | `trunc` | |

TTEST | `t.test` | |

TYPE | similar concepts in R are `typeof` , `mode` , `class` . Use `str` to understand the structure of objects | |

UPPER | `toupper` | |

VALUE | `as.numeric` | |

VAR | `var` | |

VLOOKUP | use subscripting in R | |

WEEKDAY | `weekdays` | |

WEIBULL | `pweibull` or `dweibull` | `pweibull` when cumulative, `dweibull` when not |

ZTEST | use `pnorm` on the calculated statistic |

The trigonometric functions, like `cos`

, `acos`

, `acosh`

are the same, except the R functions are all in lowercase.

### Arguments

Spreadsheets show you the arguments of a function. The `args`

function in R provides similar information. For example:

> args(sample) function (x, size, replace = FALSE, prob = NULL) NULL

This shows that `replace`

and `prob`

both have default values, and so are not required. Actually `size`

is not required either -- `x`

is the only mandatory argument.

You will learn to not even see the `NULL`

on the final line of the result of `args`

.

### Help

You can get help for a function with the question mark operator:

?sample

This will show you the help file for the object -- `sample`

in this case. It is best not to let yourself be overwhelmed by a help file.

## R vectorization

Most of the R functions are vectorized.

This is like creating a new spreadsheet column where an argument of the function is a value from the same row but a different column. Think of putting `=EXP(A1)`

in cell B1 and then filling it down.

Figure 4: EXP example of the vectorization idea, shown before column K is filled down.

Giving a vector to `exp`

returns the exponential of each of the values in the input vector:

> exp(0:5) [1] 1.000000 2.718282 7.389056 20.085537 [5] 54.598150 148.413159

The result is a vector of length 6 -- the same length as the input. The number in square brackets at the start of each line of output is the index number of the first item on the line.

## Some R resources

“Impatient R” provides a grounding in how to use R.

“Some hints for the R beginner” suggests additional ways to learn R.

## Epilogue

*And they're all made out of ticky tacky*

*And they all look just the same*

from "Little Boxes" by Malvina Reynolds (1900 - 1978)

The post From spreadsheet thinking to R thinking appeared first on Burns Statistics.

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