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Error in if/while (condition) {: missing Value where TRUE/FALSE needed
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The evaluation of condition resulted in an NA. The if conditional must have either a TRUE or FALSE result.
if (NA) {}
## Error in if (NA) { : missing value where TRUE/FALSE needed
This can happen accidentally as the results of calculations:
if(TRUE && sqrt(-1)) ...
Check if a path represents a file or a folder
I need a valid method to check if a String represents a path for file or a directory. What are valid directory names in Android? As it comes out, folder names can contain '.' chars, so how does system understand whether there's a file or a folder?
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Create a folder if it doesn't already exist
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Try this, using mkdir:
if (!file_exists('path/to/directory')) {
mkdir('path/to/directory', 0777, true);
}
Note that 0777 is already the default mode for directories and may still be modified by the current umask.
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Assign variable value inside if-statement [duplicate]
...can be assigned but not declared inside the conditional statement:
int v;
if((v = someMethod()) != 0) return true;
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Check if string contains only whitespace
How can I test if a string contains only whitespace?
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Check if a program exists from a Makefile
How can I check if a program is callable from a Makefile?
12 Answers
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How do you check if a certain index exists in a table?
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You can also wrap the statement into a IF EXISTS(SELECT * ...) BEGIN ... END.
– bounav
Sep 23 '13 at 9:10
27
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Check if directory mounted with bash
.... From a shell script, you can check for the mount point with grep and an if-statement:
if mount | grep /mnt/md0 > /dev/null; then
echo "yay"
else
echo "nay"
fi
In my example, the if-statement is checking the exit code of grep, which indicates if there was a match. Since I don't want...
地图组件（高德地图） · App Inventor 2 中文网
...s and holds the 标记 and then releases it.
This event will only trigger if Draggable is 假 because it
uses the same gesture as StartDrag.
StartDrag()
The StartDrag event runs when the user presses and holds the 标记 and then proceeds to
move their finger on the screen. It will be followe...
Test if something is not undefined in JavaScript
I'm checking if(response[0].title !== undefined) , but I get the error:
11 Answers
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