Value of previous row in CSV import via PHP - php

Question

I'm importing data from a CSV via PHP.
On some lines of the CSV, column 1 has a value, and on other lines it does not have a value. Column 2 always has a value.
If column 1 is empty and column 2 has a value, I would like column 1 to use the previous value in column 1. For example
|-------|-------|
| Col 1 | Col 2 |
|-------|-------|
| A | 2 |
| B | 5 |
| C | 3 |
| | 1 |
| D | 7 |
Would return
A2
B5
C3
C1
D7
I can use prev() on an array, but as $data[0] is a string I can't use prev()
while (($data = fgetcsv($handle, 1000, ",")) !== FALSE) {
if ($i > 0) {
if ($data[0]=='' && $data[1]!=='') {
echo prev($data[0]).$data[1]'<br/>';
} else {
echo $data[0].$data[1]'<br/>';
}
}
$i++;
}
Banging my head against a wall for hours now, so I'd love a pointer!

Answer 1

This should work as long as the first row is not empty...
$x = null;
while (($data = fgetcsv($handle, 1000, ",")) !== FALSE) {
if ($i > 0) {
$x = $data[0] == '' ? $x : $data[0];
// this is like: if $data[0] is empty then use $x else say $x is $data[0].
// Like that you can keep track of the previous value.
// If there is one overwrite with the new one else keep the old value
echo $x.$data[1]'<br/>';
}
$i++;
}

Answer 2

You can store previous value in the variable and use that
$previousColumn1 = '';
while (($data = fgetcsv($handle, 1000, ",")) !== FALSE) {
if ($i > 0) {
if ($data[0]=='' && $data[1]!=='') {
echo $previousColumn1.$data[1]'<br/>';
} else {
$previousColumn1 = $data[0];
echo $data[0].$data[1]'<br/>';
}
}
$i++;
}

Answer 3

As has been mentioned, just storing the previous value and overwriting it any time a new value is given will do the job. It will assume that if the first row is blank that the $prev value you provide outside the loop will be used...
$prev = '';
while (($data = fgetcsv($handle, 1000, ",")) !== FALSE) {
$prev = $data[0]?:$prev;
echo $prev.$data[1].PHP_EOL;
}
This uses the short form of ?: to say if there is a value for $data[0] - then use it, otherwise use $prev.