mean, colMeans, rowMeans – calc. means
使用例: mean(OBJ,na.rm=T/F)
概要:
mean OBJ全体の平均を計算（欠損値を除外して計算する場合はna.rm=Tとする）
colMeans 列毎にOBJの平均を計算（e.g. 変数毎の平均）
rowMeans 行毎にOBJの平均を計算（e.g. 被験者毎の平均）
関連: var, sd

# usage #
mean(OBJ)
colMeans(OBJ)
rowMeans(OBJ)

##### ----- examples ----- #####
> datMat<-matrix(rnorm(10),ncol=2)
> datMat
           [,1]        [,2]
[1,] -1.1604860  0.09106227
[2,] -0.3358416  0.36780023
[3,]  0.1917609 -0.62506053
[4,] -0.9900861 -0.86436989
[5,] -0.9549163 -2.05218273
> mean(datMat) #10個の数値の平均
[1] -0.633232
> colMeans(datMat) #列ごとの平均（e.g. 変数毎の平均）
[1] -0.6499138 -0.6165501
> rowMeans(datMat) #行ごとの平均（e.g. 被験者毎の平均
[1] -0.53471189  0.01597933 -0.21664982 -0.92722799 -1.50354951

# 欠損値がある場合の例
> datMat[1,1]=NaN
> datMat
           [,1]        [,2]
[1,]        NaN  0.09106227
[2,] -0.3358416  0.36780023
[3,]  0.1917609 -0.62506053
[4,] -0.9900861 -0.86436989
[5,] -0.9549163 -2.05218273
> mean(datMat)
[1] NaN
> mean(datMat,na.rm=T)
[1] -0.5746482
> colMeans(datMat)
[1]        NaN -0.6165501
> colMeans(datMat,na.rm=T)
[1] -0.5222708 -0.6165501
> rowMeans(datMat)
[1]         NaN  0.01597933 -0.21664982 -0.92722799 -1.50354951
> rowMeans(datMat,na.rm=T)
[1]  0.09106227  0.01597933 -0.21664982 -0.92722799 -1.50354951
##### ----- end examples ----- #####