[R] reshape2: Lost Values Between melt() and dcast()

[Justin Haynes]

The reason dcast would give that warning (not a failure) is if the
formula you gave did not specify unique values.  Thus, dcast needs an
aggregating function, which defaults to length.

However, the dcast calls that "failed" can be helpful for determining
the source of your error.  I'd look at the outputs of those two dcast
calls and find cells where the length is > 1.  Those are duplicated
entries in your initial data.frames (when I've run into this is was
usually due to NA values somewhere unexpected).

Hope that clarifies things.

Justin


On Mon, Oct 31, 2011 at 9:32 AM, Rich Shepard <rshepard at appl-ecosys.com> wrote:
>  Working with 5 subset streams from my source data frame, three of them
> successfully call dcast(), but two fail:
>
> jerritt.cast <- dcast(jerritt.melt, site + sampdate ~ param)
> Aggregation function missing: defaulting to length
>
> and
>
> winters.cast <- dcast(winters.melt, site + sampdate ~ param)
> Aggregation function missing: defaulting to length
>
>  Yet both data frames have the values in their .melt data frames:
>
> summary(jerritt.melt)
>      site         sampdate              param       variable
>  JCM-1  :2178   Min.   :1978-03-28   pH     : 292   quant:7519
>  JCM-20A:2149   1st Qu.:1996-05-24   As     : 286
>  JC-E   : 476   Median :2000-05-31   SO4    : 271
>  JC     : 400   Mean   :2001-02-04   TDS    : 271
>  GD-1   : 395   3rd Qu.:2006-05-31   Cl     : 253
>  JC-2   : 349   Max.   :2009-12-30   Zn     : 250
>  (Other):1572                        (Other):5896
>     value
>  Min.   :    0.000
>  1st Qu.:    0.005
>  Median :    0.650
>  Mean   :  317.588
>  3rd Qu.:   27.000
>  Max.   :20450.000
>  NA's   : 2134.000
>
> and
>
> summary(winters.melt)
>      site        sampdate              param      variable
>  WC     :601   Min.   :1987-07-23   As     : 96   quant:1189
>  WC-2   :327   1st Qu.:1994-06-15   TDS    : 79
>  WC-1   :261   Median :1995-07-27   NO3-N  : 74
>  BC-0.5 :  0   Mean   :1997-05-15   pH     : 72
>  BC-1   :  0   3rd Qu.:1996-07-29   SO4    : 69
>  BC-1.5 :  0   Max.   :2011-06-06   Cl     : 64
>  (Other):  0                        (Other):735
>     value
>  Min.   :   0.00
>  1st Qu.:   0.05
>  Median :   7.59
>  Mean   :  79.20
>  3rd Qu.:  75.00
>  Max.   :2587.00
>  NA's   : 252.00
>
>  What might be causing dcast() to fail with these two data frames while it
> succeeds with three others processed using the same syntax? If additional
> information would help, let me know and I'll provide it.
>
> Puzzled,
>
> Rich
>
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