ffill

ffill(obj, [limit])

obj is a vector/matrix/table or an array vector.

limit (optional) is a positive integer that specifies the maximum number of consecutive null values to forward fill for each block of null values. limit is not supported when obj is an array vector.

If obj is a vector, forward fill the null values in obj with the previous non-null value.

If obj is an array vector:

• For an empty row, fill it with the nearest non-empty row that precedes it.
• For null values in a column, fill them with the nearest non-null value that precedes it within the same column.

If obj is a matrix or a table, forward fill the null values in each column of obj according to the above rules.

This operation creates a new vector and does not change the input vector. Function ffill! changes the input vector.

Example 1

x=1 2 3 NULL NULL NULL 4 5 6
x.ffill();
// output: [1,2,3,3,3,3,4,5,6]

x;
// The value of x is not changed.
// output: [1,2,3,,,,4,5,6]

Example 2: Specify parameter limit.

x=1 2 3 NULL NULL NULL 4 5 6
x.ffill(1);
// output: [1,2,3,3,,,4,5,6]
                
x.ffill(2);
x;
// output: [1,2,3,3,3,,4,5,6]

Example 3: Specify obj as a table.

date=[2012.06.12,2012.06.12,2012.06.13,2012.06.14,2012.06.15]
sym=["IBM","MSFT","IBM","MSFT","MSFT"]
price=[40.56,26.56,,,50.76]
qty=[2200,4500,,5600,]
timestamp=[09:34:07,09:35:26,09:36:42,09:36:51,09:36:59]
t=table(date,timestamp,sym,price,qty);
t;

t.ffill();

select date, timestamp, sym, price.ffill() as price, qty.ffill() as qty from t context by sym;

Example 4: Specify obj as an array vector.

In the following example, the fourth row of the array vector x is empty, so it is filled with the third row [6, 7, 8]; the second element of the first column is null, so it is filled with the previous non-null value 1 in that column.

x = array(INT[], 0).append!([1 2 3, NULL 5, 6 7 8, NULL])
x
// output:[[1,2,3],[NULL,5],[6,7,8],[NULL]]
ffill(x)
// output:[[1,2,3],[1,5],[6,7,8],[6,7,8]]