Named EXCEL lambdas for one and two dimensional linear interpolation

xInterp.txt

/**Basic 1D linear generator from 2 pts*/
LEXT = LAMBDA(X,XS,YS,
    LET(X_1,INDEX(XS,1),
        X_2, INDEX(XS,2),
        Y_1, INDEX(YS,1),
        Y_2, INDEX(YS,2),
        Y_1+(X-X_1)*(Y_2-Y_1)/(X_2-X_1)
        )
);

/**1D linear interpolation, set SORTED=0 for unsorted data - presorting data recommended*/
INTERP1 = LAMBDA(X,XARRAY,YARRAY,[SORTED],
    IF(OR(ISOMITTED(SORTED),SORTED=1,SORTED=0),
    LET(
        SORT_METHOD, IF(OR(ISOMITTED(SORTED),SORTED=1),2,1),
        X_1, XLOOKUP(X,XARRAY,XARRAY,,-1,SORT_METHOD),
        X_2, XLOOKUP(X,XARRAY,XARRAY,,1,SORT_METHOD),
        Y_1, XLOOKUP(X,XARRAY,YARRAY,,-1,SORT_METHOD),
        Y_2, XLOOKUP(X,XARRAY,YARRAY,,1,SORT_METHOD),
        IF(X=X_1,Y_1,Y_1+(X-X_1)*(Y_2-Y_1)/(X_2-X_1))
    ))
);

/**2D linear interpolation, set SORTED=0 for unsorted data - presorting data recommended*/
INTERP2 = LAMBDA(X,Y,XARRAY,YARRAY,ZARRAY,[SORTED],
    IF(OR(ISOMITTED(SORTED),SORTED=1,SORTED=0),
    LET(
        SORT_METHOD, IF(OR(ISOMITTED(SORTED),SORTED=1),2,1),
        X_1, XLOOKUP(X,XARRAY,XARRAY,,-1,SORT_METHOD),
        X_2, XLOOKUP(X,XARRAY,XARRAY,,1,SORT_METHOD),
        Y_1, XLOOKUP(Y,YARRAY,YARRAY,,-1,SORT_METHOD),
        Y_2, XLOOKUP(Y,YARRAY,YARRAY,,1,SORT_METHOD),
        Z_11, XLOOKUP(X_1,XARRAY,XLOOKUP(Y_1,YARRAY,ZARRAY,,0,SORT_METHOD),,0,SORT_METHOD),
        Z_12, XLOOKUP(X_1,XARRAY,XLOOKUP(Y_2,YARRAY,ZARRAY,,0,SORT_METHOD),,0,SORT_METHOD),
        Z_21, XLOOKUP(X_2,XARRAY,XLOOKUP(Y_1,YARRAY,ZARRAY,,0,SORT_METHOD),,0,SORT_METHOD),
        Z_22, XLOOKUP(X_2,XARRAY,XLOOKUP(Y_2,YARRAY,ZARRAY,,0,SORT_METHOD),,0,SORT_METHOD),
        Z_1, IF(Y=Y_1,Z_12,Z_11+(Y-Y_1)*(Z_12-Z_11)/(Y_2-Y_1)),
        Z_2, IF(Y=Y_1,Z_21,Z_21+(Y-Y_1)*(Z_22-Z_21)/(Y_2-Y_1)),
        IF(X=X_1,Z_1,Z_1+(X-X_1)*(Z_2-Z_1)/(X_2-X_1))
    ))
);

/** 2D wrapper for XLOOKUP - Maintains access to most of xlookup's optional inputs*/
XXXLOOKUP = LAMBDA(xi,yi,xs,ys,zs,[match_mode_x],[match_mode_y],[search_mode],
    LET(
            step1, XLOOKUP(xi,xs,zs,,match_mode_x,search_mode),
            XLOOKUP(yi,ys,step1,,match_mode_y,search_mode)            
    )
);

Revised for new docstring format and improved documentation.

Depreciated... Functions now included in general toolbox