mvl_index_lapply {RMVL}

Apply function to indices of nearby rows

Description

This function is passed the index computed by mvl_write_spatial_index1 or mvl_write_extent_index and a list of vectors, which are interpreted in a data frame fashion, or an R data.frame. For each row we retrieve that set of indices that matches it and call function fn(i, idx) with index i of row being processed and vector idx listing matched indices.

Usage

mvl_index_lapply(index, data_list, fn)

Arguments

index

MVL_OBJECT computed by mvl_write_spatial_index1 or mvl_write_extent_index

data_list

a list of vectors of equal length. They can be MVL_OBJECTs or R vectors, or a data.fame.

fn

a function of two arguments - and index into data_list and a corresponding list of indices

Details

The notion of "matched indices" is specific to the type of index being used.

For an index created with mvl_write_spatial_index1 we return the indices of nearby rows. The user should apply an additional cut to narrow down to actual indices needed.

For an index created with mvl_write_extent_index we return the indices of rows with identical hashes. Even though 64-bit hashes produce very few collisions, it is recommended to apply additional cut to ensure that only the exactly matching rows are returned.

Value

a list of results of function fn

See Also

mvl_group

Examples

## Not run: 
Mtmp<-mvl_open("tmp_a.mvl", append=TRUE, create=TRUE)
mvl_write_object(Mtmp, data.frame(x=runif(100), y=1:100), "df1")
Mtmp<-mvl_remap(Mtmp)
mvl_write_spatial_index1(Mtmp, list(Mtmp$df1[,"x",ref=TRUE], Mtmp$df1[,"y", ref=TRUE]),
                                                               c(2, 3), "df1_sp_groups")
Mtmp<-mvl_remap(Mtmp)
mvl_index_lapply(Mtmp["df1_sp_groups", ref=TRUE], list(c(0.5, 0.6), c(2, 3)),
                                           function(i, idx) { return(list(i, idx))})

## End(Not run)