# [R] calculating mean matrix

arun smartpink111 at yahoo.com
Sun Jan 20 03:17:26 CET 2013

```
Hi,

This could be also done by:
#Using Arun's example:
res<- Reduce('+', split(df, grp))/length(levels(grp))
> res
#     V1    V2    V3    V4    V5    V6    V7    V8    V9   V10
#1  417.3 792.2 504.2 506.1 513.9 480.7 545.4 564.4 473.7 486.2
#2  585.8 416.6 409.5 417.8 480.1 586.4 436.1 615.1 449.8 501.2
#3  459.3 449.1 542.0 411.6 404.6 507.6 472.0 344.0 363.2 485.1
#4  591.1 448.4 482.6 464.0 554.0 374.1 567.9 450.0 477.9 488.0
#5  433.1 438.2 441.4 596.4 356.9 461.6 356.7 457.4 434.9 510.4
6 # 425.7 498.3 452.0 489.4 302.8 538.1 270.6 418.6 564.1 545.8
#7  755.1 526.4 615.2 559.9 483.3 379.7 439.3 458.8 528.5 564.0
#8  599.7 579.4 473.2 585.1 508.3 643.7 432.1 587.2 547.6 506.2
#9  471.8 321.0 375.8 394.4 355.5 434.4 532.1 640.5 490.1 619.1
#10 356.6 434.3 403.9 445.0 416.2 532.8 570.9 548.9 697.9 488.8
library(plyr)

res1<-aaply(laply(split(df,((1:nrow(df)-1)%/% 10)+1),as.matrix),c(2,3),mean)

res1
#    X2
#X1      V1    V2    V3    V4    V5    V6    V7    V8    V9   V10
# 1  417.3 792.2 504.2 506.1 513.9 480.7 545.4 564.4 473.7 486.2
# 2  585.8 416.6 409.5 417.8 480.1 586.4 436.1 615.1 449.8 501.2
# 3  459.3 449.1 542.0 411.6 404.6 507.6 472.0 344.0 363.2 485.1
# 4  591.1 448.4 482.6 464.0 554.0 374.1 567.9 450.0 477.9 488.0
# 5  433.1 438.2 441.4 596.4 356.9 461.6 356.7 457.4 434.9 510.4
# 6  425.7 498.3 452.0 489.4 302.8 538.1 270.6 418.6 564.1 545.8
# 7  755.1 526.4 615.2 559.9 483.3 379.7 439.3 458.8 528.5 564.0
#8  599.7 579.4 473.2 585.1 508.3 643.7 432.1 587.2 547.6 506.2
#9  471.8 321.0 375.8 394.4 355.5 434.4 532.1 640.5 490.1 619.1
#10 356.6 434.3 403.9 445.0 416.2 532.8 570.9 548.9 697.9 488.8
A.K.

----- Original Message -----
From: ya <xinxi813 at 126.com>
To: r-help <r-help at r-project.org>
Cc:
Sent: Saturday, January 19, 2013 9:49 AM
Subject: [R] calculating mean matrix

Hi list,

Thank you vey much for reading this post.

I have a data frame, I am trying to split it into a couple of data frame using one of the columns, say, x. After I get the data frames, I am planning to treat them as matrices and trying to calculate an element by element mean matrix. Could anyone give me some advice how to do it?

So far, I know that if I have a couple of matrices, say data1,data2,data3,data4...dataN, I can do it like this:

data=array(cbind(data1,data2,data3,data4,....dataN), c(2, 3, N))
#2 refers to row number of matrix, 3 refers to column number of matrix, N refers to number of matrices to be averaged.
meanmtrx=apply(data,1:2,mean)

but I do not know how to use the resulting data frames with cbind(). Maybe there are other better ways. Any advice is appreciated.

Thank you very much.

Have a nice day.

ya
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