Dynamic Variable Name in Loop

How do I create dynamic variable names inside a loop?

Use an array for this.

var markers = [];
for (var i = 0; i < coords.length; ++i) {
    markers[i] = "some stuff";
}

R: Read dynamic variable names generated in for loop

You may use get to do this -

library(dplyr)

for (i in 1:nrow(LabviewFiles)){
  assign(x = paste("P",i , "Onsets_PRH", sep = "_"), value = t(subset.data.frame(All_Phase, All_Phase$Phase==i) %>% 
                                                                 filter(CONDITIONS == "NULL_TRIAL",
                                                                        MISC_REWARD == 1,
                                                                        MISC_PASSIVE_FAILED == 1) %>% 
                                                                 select(Feedback_onset)))

  assign(x = paste("P",i , "Durations_PRH", sep = "_"), value = t(rep(0.5, times = length(get(paste("P",i , "Onsets_PRH", sep = "_"))))))
}

Note that using assign and creating variables in global environment is discouraged. You may also read Why is using assign bad?

How do you create different variable names while in a loop?

Sure you can; it's called a dictionary:

d = {}
for x in range(1, 10):
    d["string{0}".format(x)] = "Hello"

>>> d["string5"]
'Hello'
>>> d
{'string1': 'Hello',
 'string2': 'Hello',
 'string3': 'Hello',
 'string4': 'Hello',
 'string5': 'Hello',
 'string6': 'Hello',
 'string7': 'Hello',
 'string8': 'Hello',
 'string9': 'Hello'}

I said this somewhat tongue in check, but really the best way to associate one value with another value is a dictionary. That is what it was designed for!

Dynamic variable names to mutate variables in for-loop

As we are passing string, convert to symbol and evaluate (!!)

func <- function(i) {
   
   mutate(df1, !!i := case_when(!is.na(!! rlang::ensym(i)) ~ as.character(!! rlang::ensym(i)),
                              is.na(!!rlang::ensym(i)) & var0 != '1' ~ '4444',
                              TRUE ~ '0'))
 }

-testing

for(i in vars) {
   df1 <- func(i)
 }
df1
  var0 var1 var2 var3
1    1    0    1   NA
2    2    1 4444    1
3    2    0    0    0
4    1    1    0 4444
5    1    0    1    1
6    2 4444 4444   NA
7    2 4444 4444    1  

---

We may do this with across as well

df1 %>%
    mutate(across(all_of(vars), 
    ~ case_when(!is.na(.) ~ as.character(.), 
       is.na(.) & var0 != '1' ~ '4444', TRUE ~ '0')))
  var0 var1 var2 var3
1    1    0    1   NA
2    2    1 4444    1
3    2    0    0    0
4    1    1    0 4444
5    1    0    1    1
6    2 4444 4444   NA
7    2 4444 4444    1

Dynamic Variable Name / Increment Variable Name

This is what is called a "variable variable."
A variable definition is comprised of two parts: the dollar sign, which tells the interpreter that it's a variable, and the variable name per se, which in short is a string; I'll call it "body" here.

So, if you have $var = 'my_other_var' and $my_other_var = 'hey', you can use the string "my_other_var" as the "body" of a the variable call.

Then echo $$var yields "hey".

Here with your example:

<?php

$var1 = 'A';
$var2 = 'B';
$var3 = 'C';
$var4 = 'D';

for ($i = 1; $i < 5; $i++) {

    $varToEcho = "var$i"; // will become var1, var2, var3 and so on

    echo $$varToEcho;

}

Dynamic variable name changing in a loop

If your bash is recent enough you can use namerefs:

function foo {
  for (( i = 1; i <= 3; i++ )); do
    local -n number="n$i"
    number="$i"
  done
  printf '%s %s %s\n' "$n1" "$n2" "$n3" 
}

Demo:

$ foo
1 2 3

If you want to export the nX variables to the global scope just add the g attribute to the local declaration:

local -ng number="n$i"

And then:

$ foo
1 2 3
$ echo "$n1 $n2 $n3"
1 2 3

Note that a bash array doesn't have a limit to its size (apart the physical limit of the available computer memory):

function foo {
  local -ag n=()
  for (( i = 1; i <= $1; i++ )); do
    n+=("$i")
  done
}

And:

$ foo 5
$ printf '%s\n' "${n[*]}"
1 2 3 4 5
$ for (( i=0; i<${#n[@]}; i++ )); do printf '%s ' "${n[i]}"; done; printf '\n'
1 2 3 4 5 
$ for val in "${n[@]}"; do printf '%s ' "$val"; done; printf '\n'
1 2 3 4 5 

We could even mix the two approaches and pass the name of the array as first argument:

function foo {
  unset n
  unset -n n
  local -ng n=$1
  for (( i = 1; i <= $2; i++ )); do
    n+=("$i")
  done
}

And:

$ foo myArray 7
$ printf '%s\n' "${myArray[*]}"
1 2 3 4 5 6 7

Dynamic variable in loop javascript

You don't want to create 9 variables. Trust me. You want to create an object.

var m = {};
for(var i=1; i<10; i++){
    m[i] = "Something";
}

You can also create an array (m = []), but since you are starting at 1 and not 0, I'd suggest an object.

Javascript/React: how to create dynamic variable names for a hook in a loop?

Use an array instead:

const animations = Array.from(
  { length: 4 },
  useAnimation
);

and then reference, eg, animations[0] instead of anim0.

---

Related Topics