[R] Populating then sorting a matrix and/or data.frame

[Noah Silverman]

That makes perfect sense.  All of my numbers are being coerced into
strings by the c() function.  Subsequently, my data.frame contains all
strings.

I can't know the length of the data.frame ahead of time, so can't
predefine it like your example.
One thought would be to make it arbitrarily long filled with 0 and
delete off the unused rows.  But this seems rather wasteful.

-N

On 11/11/10 2:02 PM, Peter Langfelder wrote:
> On Thu, Nov 11, 2010 at 1:19 PM, William Dunlap <wdunlap at tibco.com> wrote:
>> Peter,
>>
>> Your example doesn't work for me unless I
>> set options(stringsAsFactors=TRUE) first.
>> (If I do set that, then all columns of 'results'
>> have class "character", which I doubt the user
>> wants.)
> You probably mean stringsAsFactors=FALSE.
>
> What you say makes sense, because the c() function produces a vector
> in which all components have the same type, wnd it will be character.
> If you don't want to have characters, my solution would be
>
> n = 10
> results <- data.frame(a = rep("", n), b = rep(0, n), c = rep(0, n), d
> = rep(0, n))
> for(i in 1:n){
>    a = LETTERS[i];
>    b = i;
>    c = 3*i + 2
>    d = rnorm(1);
>    results$a[i] = a
>    results$b[i] = b
>    results$c[i] = c
>    results$d[i] = d
> }
>
>> results
>    a  b  c           d
> 1  A  1  5 -1.31553805
> 2  B  2  8  0.09198054
> 3  C  3 11 -0.05860804
> 4  D  4 14  0.77796136
> 5  E  5 17  1.28924697
> 6  F  6 20  0.47631483
> 7  G  7 23 -1.23727076
> 8  H  8 26  0.83595295
> 9  I  9 29  0.69435349
> 10 J 10 32 -0.30922930
>
>> mode(results[, 1])
> [1] "character"
>> mode(results[, 2])
> [1] "numeric"
>> mode(results[, 3])
> [1] "numeric"
>> mode(results[, 4])
> [1] "numeric"
>
>
>
> or alternatively
>
> n = 10
> num <- data.frame(b = rep(0, n), c = rep(0, n), d = rep(0, n))
> labels = rep("", n);
> for(i in 1:n){
>    a = LETTERS[i];
>    b = i;
>    c = 3*i + 2
>    d = rnorm(1);
>    labels[i] = a
>    num[i, ] = c(b, c, d)
> }
> results = data.frame(a = labels, num)
>
>> results
>    a  b  c           d
> 1  A  1  5 -0.47150097
> 2  B  2  8 -1.30507313
> 3  C  3 11 -1.09860425
> 4  D  4 14  0.91326330
> 5  E  5 17 -0.09732841
> 6  F  6 20 -0.75134162
> 7  G  7 23  0.31360908
> 8  H  8 26 -1.54406716
> 9  I  9 29 -0.36075743
> 10 J 10 32 -0.23758269
>> mode(results[, 1])
> [1] "character"
>> mode(results[, 2])
> [1] "numeric"
>> mode(results[, 3])
> [1] "numeric"
>> mode(results[, 4])
> [1] "numeric"
>
>
> Peter
>
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