is-empty

来源： https://stackoverflow.com/questions/57029258/why-use-null-function-instead-of-to-check-for-empty-list-in-haskell

来源： https://stackoverflow.com/questions/57029258/why-use-null-function-instead-of-to-check-for-empty-list-in-haskell

问题 Is there a JavaScript equivalent to .NET's String.IsNullOrWhitespace so that I can check if a textbox on the client-side has any visible text in it? I'd rather do this on the client-side first than post back the textbox value and rely only on server-side validation, even though I will do that as well. 回答1: It's easy enough to roll your own: function isNullOrWhitespace( input ) { if (typeof input === 'undefined' || input == null) return true; return input.replace(/\s/g, '').length < 1; } 回答2:

问题 In my code, I want to check if the password field is empty . I am using the isEmpty() method to accomplish it but it does not work. Leaving the password field blank, reverts to the 2nd else-if statement and not the third. public class MainActivity extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); final EditText password = (EditText) findViewById(R.id.editText_Password); Button enter =

问题 The following link if else statement gone bad suggests not to use the formulation > any( c(5,6,7) )==0 [1] FALSE I have been using any() to get rid of empty data frames in for() loops like this: id <- c(1,2,3,4,5,6) len <- c(11.25,11.75,12,12,12.5,13.25) df <- data.frame(id,len) bin.brks <- c(10,11,12,13,14) options(warn = -1) # to turn warnings off for (m in 1: (length(bin.brks)-1)){ #subset weights into each bin; empty when m=1 temp <- df[(df$len > bin.brks[m] & df$len <= bin.brks[m+1]),] #

问题 Java 11 has added A new instance method isBlank() to java.lang.String class. What's the basic difference between the existing isEmpty and newly added isBlank() method? 回答1: isEmpty() The java string isEmpty() method checks if this string is empty. It returns true , if the length of the string is 0 otherwise false e.g. System.out.println("".isEmpty()); // Prints - True System.out.println(" ".isEmpty()); //Prints - False Java 11 - isBlank() The new instance method java.lang.String.isBlank()

问题 I have a data frame where all the variables are of character type. Many of the columns are completely empty, i.e. only the variable headers are there, but no values. Is there any way to subset out the empty columns? 回答1: If your empty columns are really empty character columns, something like the following should work. It will need to be modified if your "empty" character columns include, say, spaces. Sample data: mydf <- data.frame( A = c("a", "b"), B = c("y", ""), C = c("", ""), D = c("", "

问题 How can I check if a variable is empty in Bash? 回答1: In Bash at least the following command tests if $var is empty : if [[ -z "$var" ]]; then # Do what you want fi The command man test is your friend. 回答2: Presuming Bash: var="" if [ -n "$var" ]; then echo "not empty" else echo "empty" fi 回答3: I have also seen if [ "x$variable" = "x" ]; then ... which is obviously very robust and shell independent. Also, there is a difference between "empty" and "unset". See How to tell if a string is not

问题 I can't seem to find a simple, straight-forward solution to the age-old problem of removing empty elements from arrays in PHP. My input array may look like this: Array ( [0] => Array ( [Name] => [EmailAddress] => ) ) (And so on, if there's more data, although there may not be...) If it looks like the above, I want it to be completely empty after I've processed it. So print_r($array); would output: Array ( ) If I run $arrayX = array_filter($arrayX); I still get the same print_r output.

问题 I have an directory tree which has been passed to array. I would like to there empty folders inside this array. How can I determine empty folders like /wp-content/uploads/2014/02/ and /wp-content/uploads/2014/ . How can I delete them recursively. Here is my array array ( 0 => './do-update.php', 5 => './wp-config.php', 6 => './wp-content/', 7 => './wp-content/uploads/', 8 => './wp-content/uploads/2013/', 9 => './wp-content/uploads/2013/05/', 10 => './wp-content/uploads/2013/05/kabeduvarkad