mjhjmtu

I need to draw many nodes with labels that I can calculate from their indices. However, a small amount of them do not follow the rule, thus I need to assign their labels manually. Can I do that somehow?

MWE:

documentclass[tikz,border=3.14mm]standalone
usepackageamssymb
begindocument
begintikzpicture
 foreach i in 1,...,30
 
 node at (i,0) [rectangle,label=above:i] (vi) $i$;
 
 % here I want to make the label of node v7 to become $varnothing$
endtikzpicture
enddocument

Note: this has nothing to do with animation, I just want to create the nodes in a loop and then change labels for some of them.

UPD: I corrected MWE, as the original one was not exactly what I implied.

You can use node also, which is described on p. 250 of the pgfmanual, for that.

documentclass[tikz,border=3.14mm]standalone
usepackageamssymb
begindocument
begintikzpicture
 foreach i in 1,...,10
 
 node at (i,0) [rectangle,label=above:$ i $] (vi) $i$;
 
 foreach i in 3,6,8
 node also [label=[fill=white]above:$ varnothing $] (vi);
 
endtikzpicture
enddocument

BIG THANKS TO MAX for the edit.

Just in case you ever have wider labels: give the labels names and use their width for Max' fill=white trick.

documentclass[tikz,border=3.14mm]standalone
usetikzlibrarycalc
usepackageamssymb
begindocument
begintikzpicture
 foreach i in 1,2,...,10
 
 node at (i,0) [rectangle,label=[name=labi]above:$ii$] (vi) $i$;
 
 foreach i in 3,6,10
 path let p1=($(labi.north east)-(labi.south west)$) in node also 
 [label=[fill=white,minimum width=x1,minimum height=y1]above:$ varnothing $] (vi);
 
endtikzpicture
enddocument

ADDENDUM: Just for curiosity I was wondering if there is a simple way to make Max' nice answer work with lists. I am sure there is and leave it to others to use some xparse or other magic. Here I just want to report an irony of fate. If one goes for the built-in LaTeX check whether or not something is an element of a list, then my naive attempt fails for two digits, precisely where the simplest version of the above also starts to go wrong. Rather funny and ironic, I'd say. ;-)

documentclass[tikz]standalone
makeatletter
% https://tex.stackexchange.com/a/260921/121799 and https://tex.stackexchange.com/a/287094/121799
newcommandifmember[2]% 
in@#1#2%
ifin@
expandafter@firstoftwo
else
expandafter@secondoftwo
fi

makeatother
usepackageamssymb

begindocument

begintikzpicture
 foreach i in 1,...,10
 
 edeftempnoexpandifmemberi3,6,9varnothingi
 node at (i,0) [rectangle,label=above:$temp$] (vi) $ i $;
 
endtikzpicture
enddocument

You can use conditionals inside the foreach loop:

documentclass[tikz]standalone

usepackageamssymb

begindocument
begintikzpicture
 foreach i in 1,...,10
 
 ifnumi=7
 node at (i,0) [rectangle,label=above:$ varnothing $] (vi) $ i $;
 else
 node at (i,0) [rectangle,label=above:$ i $] (vi) $ i $;
 fi
 
 % here I want to make the label of node v7 to become $varnothing$
endtikzpicture
enddocument

If you have more labels that should be different, the code stays more readable if you use pgfmathparse to do check the conditional:

documentclass[tikz,border=3.14mm]standalone
usepackageamssymb
begindocument
begintikzpicture
 foreach i in 1,2,...,10
 
 pgfmathparse
 ifthenelse(i==3,
 "varnothing",
 ifthenelse(i==7,
 "varnothing",
 ifthenelse(i==10,
 "varnothing",
 "i"
 )
 )
 )
 
 defmyLabelcsnamepgfmathresultendcsname
 node at (i,0) [rectangle,label=above:$ myLabel $] (vi) $i$;
 
endtikzpicture
enddocument