replace Na values with the mean of the column which contains them

Hi everyone

I have a problem with replacing the NA values with the mean of the column which contains them. If I replace Na with the means of the rest values in the column, the mean of the whole column will be still the same as if I would have omitted NA values. I have the following data

de
    [,1]        [,2]       [,3]
[1,]          NA -0.26928087 -0.1192078
[2,]          NA  1.20925752  0.9325334
[3,]          NA  0.38012008 -1.8927164
[4,]          NA -0.41778861  1.4330507
[5,]          NA -0.49677462  0.2892706
[6,]          NA -0.13248754  1.3976522
[7,]          NA -0.54179054  0.2295291
[8,]          NA  0.35788624 -0.5009389
[9,]  0.27500571 -0.41467591 -0.3426560
[10,] -3.07568579 -0.59234248 -0.8439027
[11,] -0.42240954  0.73642396 -0.4971999
[12,] -0.26901731 -0.06768044 -1.6127122
[13,]  0.01766284 -0.40321968 -0.6508823
[14,] -0.80999580 -1.52283305  1.4729576
[15,]  0.20805934  0.25974308 -1.6093478
[16,]  0.03036708 -0.04013730  0.1686006

and I wrote the code 
de[which(is.na(de))]<-sapply(seq_len(ncol(de)),function(i) {mean(de[,i],na.rm=TRUE)})

I get as the result 
  [,1]        [,2]       [,3]
[1,] -0.50575168 -0.26928087 -0.1192078
[2,] -0.12222376  1.20925752  0.9325334
[3,] -0.13412312  0.38012008 -1.8927164
[4,] -0.50575168 -0.41778861  1.4330507
[5,] -0.12222376 -0.49677462  0.2892706
[6,] -0.13412312 -0.13248754  1.3976522
[7,] -0.50575168 -0.54179054  0.2295291
[8,] -0.12222376  0.35788624 -0.5009389
[9,]  0.27500571 -0.41467591 -0.3426560
[10,] -3.07568579 -0.59234248 -0.8439027
[11,] -0.42240954  0.73642396 -0.4971999
[12,] -0.26901731 -0.06768044 -1.6127122
[13,]  0.01766284 -0.40321968 -0.6508823
[14,] -0.80999580 -1.52283305  1.4729576
[15,]  0.20805934  0.25974308 -1.6093478
[16,]  0.03036708 -0.04013730  0.1686006

It has replaced the NA values in first column with mean of first column -0.505... and second cell with mean of second column etc.
I want to have the result like this:
[,1]        [,2]       [,3]
[1,] -0.50575168 -0.26928087 -0.1192078
[2,] -0.50575168  1.20925752  0.9325334
[3,] -0.50575168  0.38012008 -1.8927164
[4,] -0.50575168 -0.41778861  1.4330507
[5,] -0.50575168 -0.49677462  0.2892706
[6,] -0.50575168 -0.13248754  1.3976522
[7,] -0.50575168 -0.54179054  0.2295291
[8,] -0.50575168  0.35788624 -0.5009389
[9,]  0.27500571 -0.41467591 -0.3426560
[10,] -3.07568579 -0.59234248 -0.8439027
[11,] -0.42240954  0.73642396 -0.4971999
[12,] -0.26901731 -0.06768044 -1.6127122
[13,]  0.01766284 -0.40321968 -0.6508823
[14,] -0.80999580 -1.52283305  1.4729576
[15,]  0.20805934  0.25974308 -1.6093478
[16,]  0.03036708 -0.04013730  0.1686006