// where $A:$A is your desiredrange
​
// if cell contains specific word
= countif($A:$A,"*_ALT*") // cannot be done with an arrayformula
​
// errors
=countif($A:$A,ISERROR())
​
// loading https://www.reddit.com/r/googlesheets/comments/aplwa6/importxml_loading/
=COUNTIF(ARRAYFORMULA(ISERR(A1:A1000)),true)
=TEXT(COUNTIF(ARRAYFORMULA(ISERR(A1:A1000)),false)/1000,"0%")
​
// whitespace
=COUNTA(SPLIT(A1, " "))

// if blank, no formula
= ARRAYFORMULA(IF(ISBLANK(A2:A),"",V2) 
​
// join header row & other row by each cell with delimiter (2rows)
= ARRAYFORMULA($B$1:$K$1&" — "&B2:K2))
​
// split by line break, transpose vertically, sort, flatten by 
= arrayformula(textjoin(char(10),1,sort(transpose(split(O2,char(10))))))

// exclude first word
REGEXEXTRACT(trim(A2:A)," .+")
​
//first name
REGEXEXTRACT(A2,"^([\w\-]+)")
REGEXEXTRACT(A2, "\S+") 
​
// match text and filter range
https://stackoverflow.com/questions/42846220/regexmatch-with-regex-reference-to-cell

// custom formula
=iserror(B1)=true
​
// weekends where A1 is the first date in the column.
=or(WEEKDAY(A3)=1,WEEKDAY(A3)=7)

// list all matches from sheet 2 based on cell value
FILTER(sheet2!A:A, REGEXMATCH(sheets!A:A,A3)) 
​
// compare 2 columns for MATCHES / DIFFERENCE
=ArrayFormula(IF(A2:A=C2:C,"MATCH","DIFFER"))