[R] do calculations as defined by a string / expand mathematical statements in R

[R. Michael Weylandt]

Sorry!! meant:  apply(array,1:2,sum)/dim(array)[3]

M

On Wed, Oct 5, 2011 at 4:31 PM, R. Michael Weylandt
<michael.weylandt at gmail.com> wrote:
> Actually, this may just be a typo in your first post, but if you
> actually want to do this calculation:
>
> (array[,,1] + array[,,2] + array[,,3] + array[,,4] + array[,,5] +
> array[,,6] + array[,,7] + array[,,8]) / 8
>
> Wouldn't this work?
>
> apply(array,3,sum)/dim(array)[3]
>
>
> On Wed, Oct 5, 2011 at 4:22 PM, R. Michael Weylandt
> <michael.weylandt at gmail.com> wrote:
>> Didn't three of us give you a function (in various flavors) that would
>> do the mean for variable inputs, reading them from a list? (Though
>> David's was admittedly much cooler than mine!)
>>
>> Anyways, look into parse(text=do) with eval() if you want to go the
>> string route.
>>
>> Michael
>>
>> On Wed, Oct 5, 2011 at 4:14 PM, Martin Batholdy <batholdy at googlemail.com> wrote:
>>> Dear R-group,
>>>
>>>
>>> is there a way to perform calculations that are defined in a string format?
>>>
>>>
>>> for example I have different variables:
>>>
>>> x1 <- 3
>>> x2 <- 1
>>> x4 <- 1
>>>
>>> and a string-variable:
>>>
>>> do <- 'x1 + x2 + x3'
>>>
>>>
>>> Is there any way to perform what the variable 'do'-describes
>>> (just like the formula-element but more elemental)?
>>>
>>>
>>>
>>> Perhaps my idea to solve my problem is a little bit strange.
>>>
>>>
>>> My general problem is, that I have to do arithmetics for which there seems to be no function available that I can apply in order to be more flexible.
>>>
>>>
>>> To be precise, I have to add up three dimensional arrays.
>>>
>>> I can do that like this (as someone suggested on this help-list – thanks for that!):
>>>
>>> (array[,,1] + array[,,2] + array[,,3]) / 3
>>>
>>>
>>> However in my case it can happen that at some point, I don't have to add 3 but 8 'array-slices'
>>> (or 10 or x).
>>>
>>> And I don't want to manually expand the above statement to:
>>>
>>> (array[,,1] + array[,,2] + array[,,3] + array[,,4] + array[,,5] + array[,,6] + array[,,7] + array[,,8]) / 8
>>>
>>> (ok, now I have done it ;)
>>>
>>>
>>>
>>> So, my thinking was that I can easily expand and change a string (with the paste-function / repeat-function etc.).
>>> But how can I expand a mathematical statement?
>>>
>>>
>>> thanks for any suggestions!
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>>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>>
>>
>