string-concatenation

问题 I have a array that looks like this: $array = [ ["444", "0081"], ["449", "0081"], ["451", "0081"], ["455", "2100"], ["469", "2100"] ]; I need to group as a new array that looks like: array ( 0 => array ( 0 => '444,449,451', 1 => '0081', ), 1 => array ( 0 => '455,469', 1 => '2100', ), ) I'd tried many scripts, but with no success. function _group_by($array, $key) { $return = array(); foreach($array as $val) { $return[$val[$key]][] = $val; } return $return; } $newArray = _group_by($array, 1); /

问题 Are there differences between these examples? Which should I use in which case? var str1 = "abc" + dynamicString + dynamicString2; var str2 = String.Format("abc{0}{1}", dynamicString, dynamicString2); var str3 = new StringBuilder("abc"). Append(dynamicString). Append(dynamicString2). ToString(); var str4 = String.Concat("abc", dynamicString, dynamicString2); There are similar questions: Difference in String concatenation which only asks about the + operator, and it's not even mentioned in the

问题 Related: Strings as variable references in R Possibly related: Concatenate expressions to subset a dataframe I've simplified the question per the comment request. Here goes with some example data. dat <- data.frame(num=1:10,sq=(1:10)^2,cu=(1:10)^3) set1 <- subset(dat,num>5) set2 <- subset(dat,num<=5) Now, I'd like to make a bubble plot from these. I have a more complicated data set with 3+ colors and complicated subsets, but I do something like this: symbols(set1$sq,set1$cu,circles=set1$num

问题 Related: Strings as variable references in R Possibly related: Concatenate expressions to subset a dataframe I've simplified the question per the comment request. Here goes with some example data. dat <- data.frame(num=1:10,sq=(1:10)^2,cu=(1:10)^3) set1 <- subset(dat,num>5) set2 <- subset(dat,num<=5) Now, I'd like to make a bubble plot from these. I have a more complicated data set with 3+ colors and complicated subsets, but I do something like this: symbols(set1$sq,set1$cu,circles=set1$num

问题 I need to create a callback for <h:commandButton> while as a parameter I need to pass an argument that is string-concatenated with an external parameter id: I tried nesting an EL expression something like this: <h:commandButton ... action="#{someController.doSomething('#{id}SomeTableId')}" /> However this failed with an EL exception. What is a right syntax/approach to do this? 回答1: If you're already on EL 3.0 (Java EE 7; WildFly, Tomcat 8, GlassFish 4, etc), then you could use the new +=

问题 I need to create a callback for <h:commandButton> while as a parameter I need to pass an argument that is string-concatenated with an external parameter id: I tried nesting an EL expression something like this: <h:commandButton ... action="#{someController.doSomething('#{id}SomeTableId')}" /> However this failed with an EL exception. What is a right syntax/approach to do this? 回答1: If you're already on EL 3.0 (Java EE 7; WildFly, Tomcat 8, GlassFish 4, etc), then you could use the new +=

问题 Today, I read this thread about the speed of string concatenation. Surprisingly, string concatenation was the winner: http://jsben.ch/#/OJ3vo The result was opposite of what I thought. Besides, there are many articles about this which explain oppositely like this. I can guess that browsers are optimized to string concat on the latest version, but how do they do that? Can we say that it is better to use + when concatenating strings? Update So, in modern browsers string concatenation is

问题 I'm looking for an example code or how to improve the below code (that it's very slow IMO, but it's that I can write) to the fastest way to convert an 2D-array into a char* and copy a char to it. char* join(int c, size_t arrsize, const char* arr[]) { char *buf, *tbuf, *val; size_t i, vsize, total; buf = malloc(1); for(i = total = 0; i < arrsize; ++i) { val = arr[i]; vsize = strlen(val); if((tbuf = realloc(buf, total + vsize + 2)) == NULL) { if(buf != NULL) free(buf); return NULL; } buf = tbuf

问题 I can able to concatenate the values using the following code $sqlselect = "UPDATE billing_details SET SRF = CONCAT(Year, ID)"; but it returns the result value as "NULL". Kindly help me to solve this issue Table Structure: Year *Varchar(5)* ID *Int(10)* SRF *Varchar(100)* Result Table: Year Id SRF A 1 NULL A 2 NULL A 3 NULL 回答1: MySql CONCAT function is return NULL if any argument value if null value, see blow SELECT COCAT(NULL, 1) OR SELECT COCAT(1, NULL) >NULL If you want to keep other

问题 I can able to concatenate the values using the following code $sqlselect = "UPDATE billing_details SET SRF = CONCAT(Year, ID)"; but it returns the result value as "NULL". Kindly help me to solve this issue Table Structure: Year *Varchar(5)* ID *Int(10)* SRF *Varchar(100)* Result Table: Year Id SRF A 1 NULL A 2 NULL A 3 NULL 回答1: MySql CONCAT function is return NULL if any argument value if null value, see blow SELECT COCAT(NULL, 1) OR SELECT COCAT(1, NULL) >NULL If you want to keep other