使用R从数据框中删除NA值

Question

I have a large scale data frame with ?_? values which dimensions are 501 rows and 42844 columns. Using R , i have already replaced them with NA by using this code below :

data[data == "?_?"] <- NA

So i have NA values now and I want to omit these from the Data.frame but something is going bad.... When I hit the command below :

data_na_rm <- na.omit(data)

I get a 0 , 42844 object as a result.

dim(data_na_rm) #gives me 0 42844
data_na_rm[1,2] #gives me NA
data_na_rm[5,3] #gives me NA
############################
data_na_rm[2]   #gives me the title of the second column 
data_na_rm[5]   #gives me the title fo the fifth

What i have to do?? I've spend on this thing to many hours. I would appreciate if anyone could spend some time for this in order to help me.

Answer 1

Like what JackStat said in the comments, you might have NAs in every row. Maybe you should test for that?:

    # Some Data. All rows have an NA but not all columns

    df <- data.frame(col1 = c(NA, 2, 3, 4),
             col2 = c(1, NA, 3, 4),
             col3 = c(1, 2, NA, 4),
             col4 = c(1, 2, 3, NA),
             col5 = c(1, 2, 3, 4))

# test whether an NA is present in each row

apply(df, 1, function(x) {sum(is.na(x)) > 0})
[1] TRUE TRUE TRUE TRUE

This will help you find which columns are contributing the most NAs. It sums up the number of NAs:

apply(df, 2, function(x) {sum(is.na(x))})
col1 col2 col3 col4 col5 
   1    1    1    1    0