loops

问题 Is that really true that i can use $_ as a dummy variable in foreach loop if there is no need for $value in foreach($array as $key => $value) ? I could not find any useful information that proves this except PHP syntax formatting. There's a special case for foreach loops when the value is not used inside the loop. In this case the dummy variable $_ (underscore) is used: foreach ($GLOBALS['TCA'] as $table => $_) { // Do something with $table } This is done for performance reasons, as it is

问题 Is that really true that i can use $_ as a dummy variable in foreach loop if there is no need for $value in foreach($array as $key => $value) ? I could not find any useful information that proves this except PHP syntax formatting. There's a special case for foreach loops when the value is not used inside the loop. In this case the dummy variable $_ (underscore) is used: foreach ($GLOBALS['TCA'] as $table => $_) { // Do something with $table } This is done for performance reasons, as it is

问题 Is that really true that i can use $_ as a dummy variable in foreach loop if there is no need for $value in foreach($array as $key => $value) ? I could not find any useful information that proves this except PHP syntax formatting. There's a special case for foreach loops when the value is not used inside the loop. In this case the dummy variable $_ (underscore) is used: foreach ($GLOBALS['TCA'] as $table => $_) { // Do something with $table } This is done for performance reasons, as it is

问题 Say I have a large nested loop of the form long long i, j, k, i_end, j_end; ... for (i = 0; i < i_end; i++) { j_bgn = get_j_bgn(i); for (j = j_bgn; j < j_end; j++) { ... } } with some large i_end and j_end , say i_end = j_end = 10000000000 . If I know that j_bgn is always small, perhaps even always either 0 or 1 , is it beneficial performance-wise to use a smaller type for this, like signed char j_bgn ? Or does this come with a recurring cost due to implicit casting to long long each time we

问题 I have a series of data frames structured similarly to this: df <- data.frame(x = c('notes','year',1995:2005), y = c(NA,'value',11:21)) df2 <- data.frame(x = c('notes','year',1995:2005), y = c(NA,'value',50:60)) In order to clean them I wrote a user defined function with a set of cleaning steps: clean <- function(df){ colnames(df) <- df[2,] df <- df[grep('^[0-9]{4}', df$year),] return(df) } I'd now like to put my data frames in a list: df_list <- list(df,df2) and clean them all at once. I

问题 Im trying to loop through PHP arrays decoded from a json file. I get the results but it only gives me the first results of the arrays in the the file. How can I make it loop? This is my code: foreach ($events as $event) { echo $event['d']['Tree1'][0]['Tree2']['Field1'] . '<br>'; echo $event['d']['Tree1'][0]['Tree2']['Field2'] . '<br>'; echo $event['d']['Tree1'][0]['Tree2']['Field3'] . '<br>'; } 回答1: Sounds like you're trying to loop through the values of a "multidimensional array". You're

问题 Im trying to loop through PHP arrays decoded from a json file. I get the results but it only gives me the first results of the arrays in the the file. How can I make it loop? This is my code: foreach ($events as $event) { echo $event['d']['Tree1'][0]['Tree2']['Field1'] . '<br>'; echo $event['d']['Tree1'][0]['Tree2']['Field2'] . '<br>'; echo $event['d']['Tree1'][0]['Tree2']['Field3'] . '<br>'; } 回答1: Sounds like you're trying to loop through the values of a "multidimensional array". You're

问题 Is it possible to create a loop that creates this resources? There is a lot of repetition of the same resources. I tried using maps to create a loop but map doesn't accept anything other default block. Or is it normal to manually create all 4 resources? Just some suggestions as answer is enough, I'm trying to learn it myself. resource "aws_subnet" "public-test-a" { vpc_id = aws_vpc.vpc-test-02.id cidr_block = "10.0.0.16/28" map_public_ip_on_launch = true availability_zone = var.AZ[1] tags = {

问题 Is it possible to create a loop that creates this resources? There is a lot of repetition of the same resources. I tried using maps to create a loop but map doesn't accept anything other default block. Or is it normal to manually create all 4 resources? Just some suggestions as answer is enough, I'm trying to learn it myself. resource "aws_subnet" "public-test-a" { vpc_id = aws_vpc.vpc-test-02.id cidr_block = "10.0.0.16/28" map_public_ip_on_launch = true availability_zone = var.AZ[1] tags = {

问题 How to flip this triangle? So i was making aritmethic sequance triangle. It was upside down. How do I turn it 180 degree? for example: 1=1 1+2=3 1+2+3=6 etc... my code: package javaapplication4; public class NewClass5 { public static void main(String[] args) { int i=5,a; for(int j=i; j>=1; j--) { for(a=1; a<=i; a++) System.out.print(a +" + "); int n = 0; for(a = 1; a<=i; a++) { n = n + a; } System.out.print(" = "+ n); System.out.println(); i--; } } } 回答1: You can do it for any n, by getting