# Generalized and smart apply()/Reduce()/tapply() for data folding. ```r areduce(FUN, X, MARGIN, ..., SIMPLIFY = TRUE, SAFE = FALSE) ``` ## Arguments - `FUN`: Usually a summary function (like `all` and `sum`). - `X`: A garray, with margins (names of dimnames) and maybe with sdim. - `MARGIN`: Some margins of X and names of sdim. MARGIN=character() means to reduce all margins (over no margin). In such case, areduce() is not needed actually. - `...`: Further arguments to 'FUN', no matching of margins. - `SIMPLIFY`: TRUE - simplifies the result list to vector of atomic if possible, and triggers warning and not simplifies if impossible; FALSE - not simplifies for non speed-up function, and issues warning (and have to simplify) for speed-up function; NA - simplifies but no warning if impossible. - `SAFE`: TRUE - use safe but slow implementation, in which data splited from the array are reorganized into small arrays (as are being subset by `[]`) and passed to FUN (other attributes are dropped, however); FALSE - faster, data are passed to FUN as dimension-less vectors. ## Returns A matrix (similar to return of apply() or tapply()), with the trailing margins the same as MARGIN, while the leading margins depend on FUN and SIMPLIFY. If FUN returns a scalar or SIMPLIFY=FALSE, then no leading margins. In MARGIN, subdimension is replaced with superdims. ## Examples ```r a <- garray(1:24, c(4,6), dimnames=list(X=LETTERS[1:4], Y=letters[1:6]), sdim=list(XX=c(x1=3,x2=1), YY=c(y1=1,y2=2))) x1 <- areduce("sum", a, c("X")) x2 <- areduce(`sum`, a, c("X")) stopifnot(garray(c(66,72,78,84), margins="X")==x1, x2==x1) yy1 <- areduce("sum", a, c("YY")) yy2 <- areduce(`sum`, a, c("YY")) stopifnot(garray(c(10,68,58,164), margins="Y")==yy1, yy2==yy1) xyy1 <- areduce("sum", a, c("X","YY")) xyy2 <- areduce(`sum`, a, c("X","YY")) stopifnot(xyy1==xyy2) xxyy1 <- areduce("sum", a, c("XX","YY")) xxyy2 <- areduce(`sum`, a, c("XX","YY")) stopifnot(garray(c(6,4,48,20,42,16,120,44), c(X=2,Y=4))==xxyy1) stopifnot(xxyy2==xxyy1) b <- garray(1:24, c(3,4,2), dimnames=list(X=LETTERS[1:3], Y=letters[1:4], Z=NULL), sdim=list(XX=c(x1=2,x2=1), YY=c(y1=1,y2=1))) xxyyz1 <- areduce("sum", b, c("XX","YY","Z")) xxyyz2 <- areduce(`sum`, b, c("XX","YY","Z")) stopifnot(xxyyz1==xxyyz2) xyz1 <- areduce(identity, b, c("XX","YY","Z"), SIMPLIFY=FALSE) xyz2 <- areduce("c", b, c("XX","YY","Z"), SIMPLIFY=FALSE) xy1 <- areduce(identity, b, c("XX","YY"), SIMPLIFY=FALSE, SAFE=TRUE) stopifnot(identical(dimnames(xy1[2,3][[1]]), list(X="C",Y="c",Z=NULL))) # garray of lists, cannot use `xyz1==xyz2` etc to compare. ```

areduce function