Using apply function on a matrix with NA entries

Question

I read Data from a csv file. If I see this file in R, I have:

  V1 V2  V3 V4  V5 V6 V7
1 14 25  83 64 987 45 78
2 15 65 789 32  14 NA NA
3 14 67  89 14  NA NA NA

If I want the maximum value in each column, I use this:

apply(df,2,max)

and this is the result:

 V1  V2  V3  V4  V5  V6  V7 
 15  67 789  64  NA  NA  NA 

but it works on the column that has no NA. How can I change my code, to compare columns with NA too?

Answer 1

You just need to add na.rm=TRUE to your apply call.

apply(df,2,max,na.rm=TRUE)

Note: This does assume every column has at least one data point. If one does not sum will return 0.

EDIT BASED ON COMMENT

fft does not have an na.rm argument. Therefore, you will need to write your own function.

apply(df,2,function(x){fft(x[!is.na(x)])})

For example:

df <- data.frame(matrix(5,5,5))
df[,3] <- NA

> df
  X1 X2 X3 X4 X5
1  5  5 NA  5  5
2  5  5 NA  5  5
3  5  5 NA  5  5
4  5  5 NA  5  5
5  5  5 NA  5  5

> apply(df,2,function(x){fft(x[!is.na(x)])})
$X1
[1] 2.500000e+01+0i 1.776357e-15+0i 1.776357e-15+0i 1.776357e-15+0i
[5] 1.776357e-15+0i

$X2
[1] 2.500000e+01+0i 1.776357e-15+0i 1.776357e-15+0i 1.776357e-15+0i
[5] 1.776357e-15+0i

$X3
complex(0)

$X4
[1] 2.500000e+01+0i 1.776357e-15+0i 1.776357e-15+0i 1.776357e-15+0i
[5] 1.776357e-15+0i

$X5
[1] 2.500000e+01+0i 1.776357e-15+0i 1.776357e-15+0i 1.776357e-15+0i
[5] 1.776357e-15+0i