[R] simple problems

Gabor Grothendieck ggrothendieck at gmail.com
Thu Dec 6 23:40:04 CET 2007

On Dec 6, 2007 3:26 PM, marciarr <marcia.rocha at gmail.com> wrote:
> Hello R users,
> I have been looking through Help files and Nabble list for the answers for
> these simple questions, but it seems to be fruitless.
> 1- in a data frame with two columns, x and y, how do I get the corresponding
> value of x to, let's say, the minimum value of the y column (min (data$y)) ?

In the builtin Formaldehyde data frame find the value of carb (first column)
which corresponds to the least value of optden (second column):

with(Formaldehyde, carb[which.min(optden)])

> 2- how do I solve a simple equation? Considering the equation y= exp(-x)^12,
> I would like to find the values of x for,  for example, y=0.01, so
> exp(-x)^12=0.01. How do I do that using R?
> I know those a probably very, very simple questions, but for which I do not
> seem to find the answer.

Search between 0 and 1 for the root of the indicated function:

uniroot(function(x) 0.1 - exp(-x)^12, 0:1)

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