[R] converting a data.frame into a different table

[Jeff Newmiller]

library(reshape2) # you probably need to install reshape2 before this works
?melt

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Sent from my phone. Please excuse my brevity.

On May 30, 2014 3:07:25 PM PDT, Assa Yeroslaviz <frymor at gmail.com> wrote:
>Hi,
>
>I have a matrix of 4.5Kx4.5K elements with column- and row names
>
>I need to convert this matrix into a table, where one column is the
>name of
>the row for the element, the second column is the name of the column
>for
>the same element and the third column is the element itself.
>
>The way I do it at the moment is with a double for-loop.
>With this way though it takes ages for the loop to finish.
>
>I was wondering whether there is a faster way of doing the same
>conversion.
>
>This is how I am doing it now:
>my.df <-data.frame()
>for (i in 1:(nrow(out5.df)-1)){
>    for (j in i:ncol(out5.df)) {
>#        print(paste(" I am at position: row-", i, " and col-", j,
>sep=""))
>    a<- cbind(start=rownames(out5.df)[i], start.1=colnames(out5.df)[j],
>Value=out5.df[i,j])
>        my.df <- rbind(my.df, a)
>        }
>    }
>
>this is an example for the data I have:
>    1    2    3    4    5    6    7
>1    FBgn0037249    FBpp0312226    FBtr0346646    FBgn0266186
>FBpp0312219    FBtr0346639    FBgn0010100
>2    FBgn0036389    FBpp0312225    FBtr0346645    FBgn0037894
>FBpp0312218    FBtr0346638    FBgn0026577
>3    FBgn0014002    FBpp0312224    FBtr0346644    FBgn0025712
>FBpp0312183    FBtr0346593    FBpp0312178
>4    FBgn0034201    FBpp0312223    FBtr0346643    FBgn0025712
>FBpp0312182    FBtr0346592    FBpp0312177
>5    FBgn0029860    FBpp0312222    FBtr0346642    FBgn0261597
>FBpp0312181    FBtr0346591    FBtr0346587
>6    FBgn0028526    FBpp0312221    FBtr0346641    FBgn0263050
>FBpp0312180    FBtr0346589    FBtr0346586
>7    FBgn0003486    FBpp0312220    FBtr0346640    FBgn0263051
>FBpp0312179    FBtr0346588    FBpp0312219
>
>What I would like to get at the end is something like that:
>> my.df
>   start start.1       Value
>1      1      X1 FBgn0037249
>2      1      X2 FBpp0312226
>3      1      X3 FBtr0346646
>4      1      X4 FBgn0266186
>5      1      X5 FBpp0312219
>6      1      X6 FBtr0346639
>7      1      X7 FBgn0010100
>8      2      X2 FBpp0312225
>9      2      X3 FBtr0346645
>10     2      X4 FBgn0037894
>11     2      X5 FBpp0312218
>12     2      X6 FBtr0346638
>13     2      X7 FBgn0026577
>14     3      X3 FBtr0346644
>15     3      X4 FBgn0025712
>16     3      X5 FBpp0312183
>17     3      X6 FBtr0346593
>18     3      X7 FBpp0312178
>19     4      X4 FBgn0025712
>20     4      X5 FBpp0312182
>21     4      X6 FBtr0346592
>22     4      X7 FBpp0312177
>23     5      X5 FBpp0312181
>24     5      X6 FBtr0346591
>25     5      X7 FBtr0346587
>26     6      X6 FBtr0346589
>27     6      X7 FBtr0346586
>
>
>Sp I would like to know if there is a better way of ding it than a
>double
>for loop.
>
>thanks
>Assa
>
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>
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